If the thread in the can was good then if it was overtightened the bolt threads should of stripped as there is a lot more metal around the threads in the can to support it.
This isn't the first time I've heard of this on Orion motors either, one guy at the track today had a brand new 6.5 Orion that had poor threads and the motor moved and shredded the spur gear. The issue may be caused by the original pilot hole drilling before the thread was cut was too large.