Engines can use pressed in wrist pins (pressed into the piston, not the rod) or "free floating" wrist pins with keepers. The roller bearing is employed because of the scant lubrication available in a typical two stroke. It requires very little lubrication to function, and the open cage design allows more of the oil/fuel mist in the crankcase to contact the load bearing surfaces. The disadvantage is that the cage holding the rollers will break the moment you hit the "critical RPM" point, so they aren't tolerant to over-revving. In your case, with 3000 miles, maybe the bearing was substandard and failed, maybe it was weakened from a "high speed blast" down a hill and failed under "normal" use. Who knows?
