Suspected metal fatigue may have caused this jib failure. Micro cracking is a condition that can only be seen with the naked eye while the crane is loaded.
The problem with some of the older cranes is the steel as flexed so much that it developed stress cracking. It's hard to tell the difference between a stress crack and metallic cracking. as a result and due to the liabilities of construction, I personally don't like cranes over 20 years old.
Think about how close this was for the operator in terms of being struck by that jib and possibly having the cab ripped off the crane.