Here's my first reaction to seeing John Boyega in a stormtrooper uniform on the surface of a desert planet.
Cinematically, this is a single reaction shot, designed to orient the audience/viewer to a new scene or the beginning of a scene. Boyega rises up, gives a solid reaction, and then moves in the frame to a new perspective that does not appear in the clip.
This suggests that the actor has been knocked out, incapacitated, or is recovering from being struck or disabled in some way. His shocked demeanor supports that.
The idea that he is, in fact a stormtrooper is a stretch for me because he is considered one of the "good guys." That would suggest the Boyega is wearing the uniform as a ruse and nothing more. He put on the armor in order to escape from a situation or to pass himself off as someone he is not. Where's the helmet? Removed because this is not who he is and this is not his actual uniform? Probably.
The Internet exploded with outrage; however, in keeping with the cinematic history, using a stormtrooper uniform to escape detection or deceive the real bad guys goes back to Episode Four, which, of course, begins with a crash-landing on the desert planet that has seen so much action.
I could be entirely wrong, of course, and I'll eat my words a year from now...