I'm disappointed. I thought this was going to be about why stall doors always open toward the actual toilet. And I thought the accepted answer was going to be so the user can hold the broken door closed with his foot.
From the headline I thought that might be the topic, also.
Your theory is good, but I suspect the main reason for stall-doors to open-in is to prevent the door swinging-out to collide with other people, as with the dominant explanation for the full-bathroom door. This is likely an even bigger concern in typically cramped bathrooms than the entry hallways.
Also, to the extent that stall walls/doors are often generic hardware, reused in many cramped spaces, having the doors open inward may give designers more confidence that the swinging of the door is not obstructed by local constraints. (Allocating the rectangle footprint for the stall ensures entry works, as opposed to allocating the rectangle-plus-outward-swinging-door-semicircle).
Another lesser consideration might be that an inward-swinging door makes occupancy by more than one person somewhat more difficult.
