This is a math question I answered which has a lot upvotes. I think that is because there a lot of views ($1k$) but it haven't got any bounty. Why?
As suggested in the comments, the question was in the hot network questions list. This can be confirmed by checking the revision history1 or the timeline.2 (You can also notice that after some time it was removed from the HNQ list by a moderator.3)
About your additional question in a comment: How does a question get into the HNQ list? The details are rather complicated, but if you are really interested, a good place to start might be this post on Meta Stack Exchange.
1This feature was implemented an the end of February 2019, for older questions you cannot find out in this way whether they were in the HNQ list. See also: Now you can know if a question really hit the HNQ
2See also: How to see questions time line?
3The possibility that moderators can remove posts from the HNQ list is relatively recent, too. There is an ongoing discussion related to this feature on this site: Under what criteria should we remove questions from the HNQ list?