The list of Rhythm Styles in the edit window do not actually set the rhythm style that the iReal Player will use - you choose the rhythm style for the iReal Player after you've saved & closed the edit window.

The list of rhythm styles in the edit window are really only for putting the name of a style as text at the top of the chart. That list includes all the ones that the iReal Player can play, plus additional ones that have been added (by the developers, I guess). You can actually add your own if you want. Think of it as info for other musicians if you're playing the chart live, instead of using the iReal Player.