That deep carve you were doing, was that draft, normal, best, or optimal? Was that the 1/16 deep carving bit?
Now that I look closely at your picture, I think I see what happened. The 1/16 deep carving bit is fexible (too flexible). When cutting to the right, it can "dig in". This happens right away if you carve with the grain. This is why it cannot be used with the rotary jig. I think the bit bent and dug in and that is when the belt slipped. See the notch in the carve where the shift started. You are lucky the bit did not break.
You were using the 1/16 deep bit - right??