My first thought was that the lower bolt had hit the guard but for that to happen the bag/bracket would have had to flex about 1.5-2" inboard. I crawled around under the bike for a while and finally found a small mark on the bottom of the bracket which is what makes me think that's what hit.
I don't put much weight in the bags. I stood on some digital scales Friday then picked up each "bag liner" and the scales didn't even register a difference. I agree, though, the belt guard did its job and I'd much rather it get blasted than the belt itself. Now to start working on a new fix...
2014 Triumph Tiger Explorer
2008 Yamaha XT250
2005 Honda CRF70F