When you did the outside loop, you lost too much airspeed at the top, and your wing tip stalled--just as you said it does anytime you get too slow. It really doesn't matter what makes you go slow, if the plane has a tip stall tendency, it's going to snap on you when you get it too slow. If you used a lot of elevator (which I suspect you did), then you probably had close to zero airspeed at the top. Once in the spin, you apparently didn't have enough altitude to come out. A spin is really a type of stall condition, that is usually recoverable from, but sometimes not. To get out of it, some planes just require coming off of the control surfaces, and they will recover on their own. Some require opposite rudder and (as Ken said) down elevator. Down elevator gets the airspeed back up where the control surfaces are effective enough to fly the plane out of the spin. Some planes even require throttling down--to minimize the gyroscopic effect of the engine. Then opposite rudder, then down elevator, then reapply power as you pull out. It all depends upon the plane. This is why it's a good idea to be very high the first time you intentionally put a plane into a flat spin, so that you have time to try different techniques, should the plane not want to come out of the spin.
Anyway, yours wasn't intentional, and you were too low to do anything about it. Next time, make the loop a bit bigger so that you can keep the airspeed up all the way through the maneuver...

FWIW, I'd call what your plane did a spin. Maybe not a flat spin, but a spin none the less. It was induced by the snapping of a wing caused by too little airspeed. Some planes just don't play nice....