Yes, that sounds like a pinched tube, most likely, especially that you found a slit on the tube where it blew..
Best way to avoid that is to sprinkle a little bit of talcum powder all around in the tire interior and on the innertube so the innertube can more easily slip in place/in position and not hang up between the bead and rim after it is mounted.
Maybe you should avoid having them mount your tires the next time. I always mount mine myself so I can be sure such things do not happen.
Chombi
Last edited by Chombi; 03-15-12 at 05:07 PM.