I'm fairly new to SE, but I've noticed a lot of questions that are "bumped" back to the top of the list, yet when I view the question there's no visible activity with a recent timestamp. In some cases, the question, answers, & comments are all from 2011 or 2012.
Are answers being bumped because someone up-voted an answer or comment? Or do questions only get bumped when an answer, comment, or other edit is added?
Questions are only bumped by edits, bounties, new answers, and the Community User if unanswered. Comments do not bump questions.
However, because of favorable google rankings, stack exchange sites attract a fair amount of spam, noise, thank you posts, and other nonsense. Good moderation means this 'content' often doesn't stick around for long, but it has the lingering effect of bumping the questions that attracted it.
If it says an actual user instead of "Community", there's a good chance it was bumped by a new answer, but that "answer" was such a bad one that it was deleted before you saw it. Deleting those answers don't un-bump the question.
If you can give a link, anyone with 10k rep can see deleted answers to confirm if that is what happened.
