This is a case where an edit to their question has stranded your answer to their original question. The same edit has included an answer in the area reserved for questions.
The solution to both situations is to rollback their edit which I will do now. I have not checked to see whether you have the privilege to do this too but I would expect that you do.
The site was designed one way. You want it to look another way. This is what Cascading Style Sheets (CSS) are for. You can either tweak your user agent (browser) style sheets, or use an extension such as Stylish to manage your style tweaks.
Here is a Stylish style you can use, makes the accepted answer background color a bit more saturated:
I don't really have an opinion one way or the other as to whether it's too subtle. Maybe? I generally find that it's just a part of new/infrequent user mentality. Some people just come for answers and don't really care much about the community aspect of the site or other features. If someone gets noticed as having asked a few questions without accepting ...
Options, from strongest to weakest, include:
Edit the answer.
Provide an answer of your own specifically countering the accepted answer.
Comment (politely) on the answer.
Downvote the answer.
Any combination of these can be applied.
Moderators are not intended to arbitrate questions of fact or accuracy. The expectation is that through the mechanisms ...
While CSS can be used by people to enhance their own GIS-SE experience, I think requests such as this one would slightly improve the user experience of anyone who would prefer to use our site without resort to configuration or customisation.
On Meta Stack Exchange there is a feature request that I made which I think would help in this situation: Keeping special status for Accepted Answers without sticking them to top forever?
It proposes that the Accept status should age away without loss of awarded points, and remain renewable by the question asker.
As far as I can tell, the system granted the bounty to that answer under the standard bounty rules, which state that if you do not designate an answer for the bounty within the deadline (plus about a half day grace period), then the highest-voted answer will get half the bounty.
No users (including moderators) can change this.
For details and more ...
Just thought about this today. So many questions with great answers, which are not accepted. I am a bit sad this idea is declined. We have voting for closing questions. Why not to have moderators in same manner vote to accept answers. Surely there is a way to filter out and prioritize not accepted answers after some time, and based on number of up-votes for ...