+1 Unhooked rims are fine, but you have to be more careful on seating the bead properly, and inflating with a floor pump (not an air compressor). I used to run 110 psi on Michelin Elans in the mid 1970s on my Araya unhooked rims. Didn't know better I guess. Put a lot of miles on them, never had a problem. But I didn't own an air compressor either (poor college student back then).

I've had a couple of failures like yours above, both times, the bead was not evenly seated, and both times I used my air compressor. Since then, I am more careful.

+1 Check for pinch flats (tube under the tire bead).