I mean, it makes sense (funnily my shower room also looks like that.) The side with the smaller tiles is where you have the shower head. The one where you have the fancy marble-pattern tile is the side directly across the glass divider, and the floor is...well, the floor.
It's also logical; if your water line leaks or needs to be replaced, you just remove the smaller tiles, which is less prone to breaking (and if it breaks, cheaper to replace than the larger sized tiles) so you can patch it up back easier.