To quote the relevant points of the ever-useful FAQ (useful to me, at least, as it contains explanations for many of Stack Exchange’s workings) regarding the community user:
Randomly poke old unanswered questions* every hour so they get some attention
* Questions with at least 30 days of no activity, at least one answer scoring zero, and no answers scoring above that. Questions that are locked or closed will not be bumped. The Community User will only bump a maximum of one question per hour.
If I was to imagine a good or useful scenario to explain what you saw, it would be a qualifying question (as per above) that came to the attention of someone who read it and believes that the existing answer served no productive purpose (perhaps it was a request for further clarification and should have been an comment?) and this either flagged or directly voted to close it. Perhaps the question as written qualified for one of the existing (or a custom) close type; perhaps not. Vote your conscience while in the review queue; may I suggest Learning the art of the review queue ?
Otherwise, for the community-bumped questions, here are the steps I take when looking at them:
Does the existing answer show evidence of answering the question? It won’t be upvoted or accepted, but perhaps the OP left a comment with a clue. It’s likely that the OP is now inactive, or else they would have accepted or upvoted the answer. I would consider upvoting the Answer to get it out of the Community rotation.
Otherwise, does the question seem answerable in its current state? If it fits a close-type, consider a VTC. (Then we’re back where you started!)