My bet is something was lost in translation. What they probably meant was only MP3 files were supported on the memory stick.
I'd leave it at that and test a few sticks with MP3 files formatted to FAT (see google if you must) as well as start with the 2GB stick.
I have a Suzuki sx4 car, which will not play any music on my memory sticks. I have at least five usb sticks from 2gb to 64 gb. The garage says it will only except a mp3 usb stick, but I know nothing about this sort of thing. What sort of memory stick will I need to buy to put music from my pc onto it to play in my car.? I have heard of mp3 players, what is the difference between mp3 players & mp3 usb sticks Please, ?