People memorize minor details of netizens (esp in grudges)?

One thing about internet culture I absolutely cannot comprehend.

I lost my password and username to an old online forum years ago. Because I was getting back into comics, I decided to create a new account and join.

When I created a new VS thread, suddenly one guy who I didn't know started flamebaiting me. I asked what was his problem and he stated that "I'm back". I told him that while I had registered on this site before, its been years since I logged in and I already lost my older username and password.

Suddenly he started calling me a username and it didn't ring a bell. He started bringing old topics I don't even know what the hell he was talking about until I researched the alias he called me and I realized it was my old username and those arguments were threads we had aggressive debates in........ That took place over 5 years ago!

Here's the thing the guy openly admitted in a recent thread that not only has he not been into contact with relatives, he actually admitted he doesn't even remember the name of his hometown nor does he recall where his brother moved to. In fact he doesn't even care about getting into contact. Yet he has the never to literally remember some 5 year old threads as though they happened yesterday and he memorized my MO and writing style to the point he immediately detected it was me (even though my writing has improved tremendously and I changed a lot of bad writing habits I used to have such as using slang like ain't)!

Update : n another example in an old gaming forum I still frequent, some members were literally bringing back things said years ago and mocking another member who was on vacation. In fact one of them was mocking the offline member because he "wanted to dress as Lawrence of Arabia". I actually decided to read the post made by the offline member and he never said he wanted to dress as Lawrence of Arabia but he's a fan of cinema and thought Lawrence of Arabia's costume was fantastic.
Update 2: Still I was absolutely at a loss of words because that post was made like 10 YEARS ago! Yet longtime members could remember parts of it like it was their social security number?! (And yet hilariously get the rest of the post's contents entirely wrong!)?

But these members are not only in their 30s but they don't remember it was Thanksgiving (I'm not lying about this!) yet they literally memorized the usernames of most members and even their email addresses and Xbox Live/PSN accounts!
Update 3: They have the nerve to memorize small posts that happened years ago but they don't even realize Thanksgiving just happened like 2 weeks ago?!

This is what I noticed. Internet forum users remember all the bits of details of other members that they can spot a member who was banned 12 years ago just by their first post in a newly registered account (despite not being on the forum literally that long and changing their online MOs a good deal).

They have the nerve to memorize small posts that happened years ago but they don't even realize Thanksgiving just happened like 2 weeks ago?!

This is what I noticed. Internet forum users remember all the bits of details of other members that they can spot a member who was banned 12 years ago just by their first post in a newly registered account (despite not being on the forum literally that long and changing their online MOs a good deal).

Yet they don't even know important details about their irl relatives and friends such as where their high school/college buddies moved to after graduation and even the house address their parents are living in (and mind you this is the very same house they GREW UP IN until they went to college!!!)?! Many don't even have their siblings phone numbers!

Yet they can memorize details of members that they can spot them just by a single post or what they state in their profiles?

It isn't exactly an internet addiction topic but I have a question. Is this tendency for people on the internet to memorize everything from the most minor details of another posters' writing style (such as making paragraphs after every three lines) related to internet addiction? Especially in grudges?

I ask because so many people who tend to memorize a member's MO on other forums I been to tend to spend excessive time online (like 4-8 hours a day) posting on various message board and indeed most internet grudges I witnessed (including some I've been a victim off unintentionally) that borders near obsession (to the point just because newly registered member else shares similar interests, they'll automatically accuse new member of being a dupe) tend to be waged by people who seem to be on the internet almost 24/7!

Yeh, they're all mentally sick people that takes pride on the psychological issues they have. I mean, I'm posting on an Internet Addiction Forum - which, I'd like to say, it's kinda funny - so I have issues too, but I'm trying to fix them. Some people are too far gone, so they just surrender to their bad habits. They no longer have a life, life is virtual for them now, so they feel the need to have virtual grudges.

Kind of sad if you ask me.