Sometimes it can be hard to go back and be sure of what happened. FWIW, had the same thing happen to me last week. Loose fitting tire. I was sure I had it on the rim, and probably I did, but must have knocked things out of whack before pumping. I went up to 30, then started to go for 60, and wham! The tire came unseated and the tube spilled out all over -- thankfully without popping. I deflated the tube, remounted the tire, and took more care the second time to ensure the rim was centered within the tire, paying close attention to the bead seat line, and all was good.