You should probably stop thinking of the internet as a whole and particularly this comment section as a place where people come with good intentions to debate. The site gets linked all the time on communities were trolling is the favorite pastime, and throwaway accounts coming to mess around aren't uncommon. All the staff is tired of that, and that's why they delete any short and dismissive comment - particularly ones among the lines of "X is bad unlike Y; Z should stop being wasted there". 4chan has already managed to turn all animation arguments into pointless duels. Won't happen here. That's one of the few Actual Policies we have when it comes to this.

To illustrate the point, just a few days ago I was talking with a Steven Universe staff member who was amused about a certain subset in this site quickly dismissing any modern piece of western animation. The comments individually weren't a huge deal and could be interpreted as not hugely antagonistic, but he was perfectly right in noticing that trend. Moments like that make me feel like we'd be better off without the system to begin with. If it weren't for the very rare worthwile argument and because they're extremely useful to leave sources for the cuts, I'd be glad to get rid of comments altogether.

Anyway, can't speak for what happened in those cases, but as far as I can tell it was all different people. I'm not hugely worried about policing which mod does what because comment deletion is as vanilla as moderation gets. Antagonistic ones are dealt with without paying much attention to it. Sometimes unnecessary chains of long resplies are deleted because they make the Latest Comments unusable so people might miss the actually important sourcing replies. Jokes, even ones by the staff, get nuked sometimes. And entire threads are lost when uploads get remade with a better source. Don't think of the replies as a permanent forum discussion because they sure as hell aren't.