I've noticed that many Reddit users with the username format Word_Word_Number (for example Absolute_Bot_1230) are almost guaranteed to either be a bot or extremely inflammatory -- it's like everything they post is meant to generate controversies.
Yeah reddit has a name generator that you can choose from when you create an account and that's the format it uses. Those names are almost exclusively bots and throwaway/anon accounts
It's Reddit's automatic username generation, so either yeah, bots, or someone logging in through Google/Facebook and having a username assigned to them.