Nope, the bolts came out cleanly... So yeah they had to have backed out. I guess the only real question is: How/why did this happen? And how can I best prevent if from happening again?
I suppose there is a very tiny possibility that I just completely forgot to tighten these bolts down in the first place... But with as careful as I was building these things, and following every single step, I can't imagine such a huge oversight.
