I'm not trying to downplay your serious and scary situation, but once upon a time, my LBS told me that an inner-tube could be inflated about fifty percent over its rating before there was risk of damage/burst.

Is it possible that you just had a bad tube and/or tire? I also noticed once that I didn't get the floor pump totally engaged on the valve, and when I filled to my target psi, I hadn't done it right - the tire didn't look or feel right, and when I rechecked the pressure, I was off (but I don't remember which way).

Glad it didn't burst on you while you were riding or in the garage! That's scary!