I have noticed people complaining about this. Looks like a normal newbie who, after a few days of browsing, decided to post several comics in quick succession, then nothing again. Not necessarily bot behavior, since they post in the correct community and the comics are relatively funny and do not ptomote anything.
But then I noticd that there's several such accounts.
It's a mystery. One that might be solved by looking at the users' IP addresses. I can't, but mods or admins can. So I'm going to trust their judgement.
Some transparency would be appreciated though.
Edit: this community has only one mod. I looked at their posting history; they apparently made a web app to make the lives of mods easier. I also read them mention somewhere that they'd have preferred to just remove an offending comment, but the admins decided to ban that person completely. Maybe these are partial answers to the question OP asked.