Interesting. Sounds like their pylon maintenance practices may be lacking. While there is only about 4 square inches of surface area holding the pylon onto the wing, it would take a lot of force to disengage the hook mechanism allowing the pylon to separate from the aircraft. These pylons are designed to separate from the wing should the pilot deem it necessary. Under normal flight conditions, initiating the pylon ejection sequence sets off two explosive carts that create a gas pressure great enough to open that hook.
I would be very interested to see the results of the investigation of this incident.