Not sure I would call myself a power user. While I did have a few posts over 50k, I was not exactly creating a ton of content. Still got an email though and decided against investing.
My few posts were almost exclusively in my local sub and plant identification, I never had a post crack 1000. Almost all my karma came from comments. Since I also got the offer, I'm guessing the bar was set very low
I think everyone got it out eventually, but I know they rolled it out in stages based on total karma. The more karma you had, the earlier you got the IPO email. And they didn't distinguish between post and comment karma. I had almost no post karma, but 402k comment karma (mostly from account age), so I got emailed pretty early.
Similar story, though I had over 100,000 karma, I never made any posts. It was all comment karma. I got invitations on both my accounts, even though ones been retired for years and the other I stopped using after the bullshit last year.