Looks like it was overtightened to me you could even see where one side of the ferrule is straight and the other is a little bent. Could of led to the issue,they say to use teflon on the ferrule. I also think that if teflon was used they wouldn't of had to kill it like they did.. Nice job on the repair by the way..
Got this from FlowGuard Gold CPVC tech manual...
Brass compression ferrules
CPVC pipe can be used with standard brass ferrules to make compression connections.
The O.D. of copper tube size (CTS) CPVC pipe is identical to that of copper. We
recommend that Teflon (PTFE) tape be applied over the ferrule to allow for the
dissimilar thermal expansion and contraction characteristics of the metal ferrule and
the plastic pipe that could possibly result in a drip leak over a period of time. Do not
over-torque the compression connection as over-torquing may result in a cracked
pipe. Non-metallic or nylon ferrules are not recommended.