Why is there a bounty? I already found the frame in question. I am confused
Occasionally a high rep user may create a bounty on a question with an existing answer marked as correct as a way to reward a newer user for an excellent or unusual answer. The result is the equivalent of the high rep user gifting some of their reputation points to the target user.
The bounty is automatically open for 7 days and as far as I know there is no way to end it early. When the bounty ends, the user who created the bounty has a window during which they can manually award the bounty to a particular answer. If it is not manually awarded, the system awards it automatically according to the rules listed above. Note that the manual award does not have to be to the answer marked correct, or the answer with the highest votes.
I've looked at the history of this question and a related post in our Velodrome Chat. It seems @Criggie decided you should get an extra bonus for identifying a random BMX frame since that is rarely accomplished when we get these kinds of questions.