The "reddit mod" the comment you're responding to would be one in charge of a particular subreddit, not of the entire network (the latter would be an "admin" in reddit parlance).

A quick perusal of https://www.reddit.com/r/SubredditDrama/ should be sufficient to understand that subreddit mods indeed do go on power trips of capricious banning, including for the grievous sin of mentioning a competing subreddit.

Wym? This happens all the time.

Many of the popular subs will retroactively ban users for posting in other subs.

I was banned from a fair amount of subs because I had a trivial argument with a mod in one sub. IIRC it was literally an "argument" about humidity being worse than dry heat, lol.

Seeing this repeated on twitter, even if its for a day, is alarming.

Reddit bans for linking out to alternative communities. Facebook blocks links to sites it finds problematic, even in private message.