KX 125 engine blow out?

I was riding my Kx125 the other day on a straight away and i got my bike into 6th gear almost wide open. i was only in sixth hear for about 5 seconds and then my bike started slowing as if i slammed in my brakes. When my bike was stopped i was able to walk my bike easily in first gear. Is this because i blew out the piston and piston rings because when i moved my kick start with my hand it felt like there was no compression in the cylinder. Also when i took out the spark plug the ground strap was blown off and so was the tip of the electrode. Did my engine blow up because of the spark plug or because of the piston and piston rings?