I think that when a band uploads content in mp3 (on bandcamp), the flac download is still mp3 quality (in a flac format) (maximum quality) if you know what i mean(am i right?). I always wanted to analyze soundfiles to better see quality of file.
You can not upload MP3 to Bandcamp, they only take lossless formats. I mean, you could take an MP3 and convert that to WAV or FLAC, and then upload, but I hope not many musicians do stuff like that, and Bandcamp is pretty clear about it in their documentation.