Airbags do release a fine powdery/smokey sort of residue. I think it's partly from the propellant and partly from cornstarch or something similar used to keep the bag material from sticking to itself, but I may be wrong about that.
Airbags inflate too quickly for you to see them. At least in my experience (twice, unfortunately, though fortunately with no significant injuries or lasting problems), they also deflate pretty quickly, so that they're at least partly deflated before you have any hope of collecting your wits about you and understanding exactly what all just went down. It is probable, in my humble opinion, that the airbag did at least somewhat contact you, and probably helped cushion your head and body somewhat (along with the seatbelt, of course).
The welt on your hand could be from the airbag sliding past it, rather like a rug burn, or it could be from the hand being propelled into something else like your head or something in the vehicle interior.
I'm very glad you're not really worse for the wear. I have no desire to be in any sort of an accident with my RV, even beyond any other vehicle, since there are so many odds and ends in cabinets and shelves and such that could quite conceivably become airborne missiles. If the latches aren't enough to keep a watermelon in the pantry on a moderately sharp corner (and, by experience, they aren't), I don't think they'll keep the dishes or books in the overhead cabinets in an accident.