It got caught under the bead. Just below and to the left of the stem in the 1st picture, is a little v-shaped gouge in the rubber, looks like a fingernail mark. That's where a little bit of the tube got under the bead, and popped when it pulled loose. You've said you deflated, shipped, and re-inflated these wheels a few times, right? If you take it all the way flat, 10 psi was mentioned, then when you re-inflate, you almost have to treat it like a fresh installation, WRT making sure the bead is clear and seated properly.

I had the same thing happen, same tube, same size, about 15 minutes after a ride. I'd decided that 65 psi on my SS was too low, and tried out 80. The ride wasn't as smooth, but the bike was faster. Did about 12 miles, and put it away, 10 minutes later, i heard a bang from the garage, that was so loud, I thought the whole bike rack had fallen over.

On my tube, i could actually make out the threads from the tire casing embossed in to the rubber.