IPA does not dissolve plastic. The bets explanation I can come up for is that there was a crack halfway through the plastic. Then the IPA leaked into that crack and expanded as it evaporated, which together with the constant pressure made the crack go all the way through rapidly and create a shockwave.
I would very much like to say a proper sharp close-up. (Macro picture taken on a good camera.)
Yes. That's what I'm thinking.