Microsoft Defender now apparently reports the infection of a artist information.
There has never been a verified report of MusicBee having had any part in a computer getting infected by malware.
Never.
So I can only do some wild guessing here.
IF the file in that temp folder was retrieved by MusicBee, it could be that the search engine for artwork (Bing) retrieved the image from a website that besides artwork, also contains warez. (there are some of those)
In theory (but I believe it is only a proof of concept, and it has never caused an actual infection anywhere) an image file can contain malicious code.
So perhaps such an image file was retrieved, and your anti-virus software suspected it might contain malicious code.
That suspicion could be a false positive though, and even it had some ground, the image would not have been able to do any harm.