Well iTunes does album art its own way, so it is likely to give different results to rockbox.
According to the manual rockbox looks for album art through a list of different places, in order, so if it doesn't find it in the earlier locations it will pick up whatever it finds elsewhere. Maybe its finding something in the parent directory?
I'd guess it's picking up something that is a 'hidden file' for windows, so you can't see it (as I think .folder files are).
The pictures can be named a number of different ways, and placed to a number of different locations. You can have pictures specific to the file or the album or use a generic picture. You can place the picture in the same directory as the file, in the parent directory or in a fixed directory named /.rockbox/albumart/. The order Rockbox uses when looking for a picture is as follows (a list in braces means that those file extensions are tried in that order):
1.
embedded (JPEG images in ID3v2 or MP4 tags only)
2.
./filename.{jpeg,jpg,bmp}
3.
./albumtitle.{jpeg,jpg,bmp}
4.
./cover.{jpeg,jpg,bmp}
5.
./folder.jpg
6.
/.rockbox/albumart/albumartist-albumtitle.{jpeg,jpg,bmp}
7.
../albumtitle.{jpeg,jpg,bmp}
8.
../cover.{jpeg,jpg,bmp}