Hi Mike,
on Yamaha keyboards, the File Selection displays are always "filtered". This means in the Style Selection display you can see only Styles, in the Registration Selection display only Registration files, and so on. (FOLDERS appear in ALL the File Selection displays, but if you are in the "wrong" section, a particular folder may be "empty".)
To open display Styles that are on a USB stick touch the Style section in the Main display > User > USB 1. Alternatively you can press one of the Style category buttons (and touch "User > USB1" then), or you can press "Expansion/User" button next to the Style category buttons.
Best regards,