I read somewhere that he did that in order to help those that were very close to Legendary rank but at the introduction of merit system they were short on activity. Reasonable decision as it's not easy at all to get 500 merit and I I'm sure those affected were in quiet a shock. I know I would be in the similar situation.
Yeah, if you were around when the merit system was rolled out (very unexpectedly, because there was no talk about it beforehand) and were a Hero member with enough activity to get to Legendary and were just waiting for the week when you'd rank up, you probably were pulling your hair out when you discovered that you now had to earn 500 merits to get there.
I tend to forget that a lot of newer members here don't realize that the merit system wasn't always a thing, that it's only been around for just over 3.5 years. OP already got his answer, so I won't repeat it. I'm sure if you go back to threads from 2010, you'll see that most of the members who posted have merit counts that represent exactly what was airdropped in Jan. 2018. And man, if you go back that far, it'll seem like the forum was a completely different one. There weren't signature campaigns back then, and I think the moderation was a lot less strict.