Do not be scared. It has happened to us all.

As far as what happened. It sounds like a secondary tip stall. That in itself is unusual, but not impossible, for a 4*.

Coming out of the stall turn, you had power off, diving at the ground and simply misjudged the point to start to pull out. It happens so do not sweat it. You probably panicked, pulled full up elevator and the plane simply stalled. It stalled so fast that the wingtip stalled first and then you have a rollover, without airspeed and altitude and the rest is history. I would also make sure that the elevator halves are moving the same amount. If the 4*60 has seperate control rods on each elevator half, they may be slightly misadjusted. If they are joined with a wire inbetween, then it's still possible they are misadjusted.

If they are misadjusted, the one that is moving up more than the other will cause a tip stall to the side that is moving more causing the plane to roll to that side in a stall.

Apologize allot to the owner of the trailer, offer to fix the damage, fix the plane and go fly it again. (Sounds like you have done all of this already).

Now when you do the stalls again, just remember to pull out a little higher and at the same time as you start to give it up elevator, start rolling in power.