Can't speak for this specific situation, but Discord does breed that a little. It's a forum where messages get lost really easily and conversations can disappear in minutes. That gives people the impression that anything they say will get forgotten so they don't need a filter, but they don't notice that it doesn't mean nobody's going to read it or that venting too much might become addictive.
A forum I'm a regular on had to institute a rule against gossiping on its discord because it was really getting out of hand. People would discuss the behavior of users there, then take that grudge back to the forum, and the user who's completely out of the subject would get confused and frustrated with the responses. It's really tempting to go on the venting area and go 'ugh does this user need to be so mean' but it's easy to fall down that trap and start talking about everyone... And not taking it to the mods if there's really a problem happening.