I don't think it is an internal puncture, as others said these hookless rims are the problem with overinflation.
I spoke to the local shop that said they never heard of an innertube blowing due to overinflation.
Also they get $37 to put an innertube in that they get $17 for. I don't know how they can pay their expenses around here. But I can't afford to spend too much after spending $35 on a wheel truing.