I heard a rule that if the dev does not give any status updates in 3 months it gets the abandoned tag, is there any truth to that?
That's what typically happens yes, though I'm not sure that's exactly a rule (perhaps more of a guideline that the moderators follow?)
For instance, there have been games which hadn't gotten any status updates from the dev over 3 months, and they had gotten abandoned tag because someone reported (to the moderators) that the said games should be tagged abandoned.
Given the vast number of games on this website, I guess they might miss out on some.
But just because it gets tagged as abandoned on this site, it doesn't necessarily mean the game is actually abandoned (sometimes it's true, but sometimes it isn't).