What could have happened to your boot is if you got that side down in the gravel, such as got stuck or riding a sharp ridgeline.

I was riding in the dunes and I thought it was a good time riding the ridgelines of the steep dunes. I got stuck while riding the ridgeline which burried the left wheel and CV shaft and the next morning I noticed I had a ripped left CV boot also. I blamed it on the sand tearing the boot. It hasnt happend in a couple years since I stopped riding the ridgelines.. And hasnt happened to any of my friends, which didnt ride like I was...