Sometimes, people tend to merit for a joke, because it makes them feel funny, help them release stresses from trading, or something like that.
Merit abusements or un-abusements on perspectives of each person, despite of the fact that sending 50 or 100 merits to one-line, joking post most likely merit abusements or at least merit inappropriate usages.
I agree with you that theymos wrote that he don't care about that, because with airdropped merits, people can not abuse for too long, and he tend to leave it naturally happen. Of course, for some extremely abused cases like sending 90 or 100 merits to some accounts to boost it to Full Members are very bad abusements.
And, if they abuse like this, they can not go much further. They can go to Senior Members with 240 or 250 merit points abused but they won't be able to move to Hero or Legendary for sure.
There are no "real" rules for giving merit ( I see subsequently it was found to likely be his alt so that is likely abuse). I mean it is not supposed to be given out on political grounds, but of course that is observably not the case. Free choice certainly applies.
There are several instances where large amounts of merit are given out from merit sources for a low value one liner.
https://bitcointalk.org/index.php?topic=5123752.msg50280347#msg50280347I have seen people just more or less ask for some merit and a merit source has just given it to them for fun.