Another possibility is that he fired one handed and the pistol wasn't properly supported during recoil, thus causing the stovepipe. If we're going to second guess, this would be the frontrunner.
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There is a reason for testing/training with a pistol by shooting from poor, unsupported, and unconventional positions. A quality firearm with quality ammo, adequately maintained (lube is almost always going to be more important than cleaning; a pistol or AR that won't go at least 1000 rounds without cleaning is broken and needs immediate attention), should not malfunction under such circumstances. There is not near enough information to determine what happened, and my guess is that it would (or at least should) be in the police reports, but the media would not care enough about such details to report it. Such would certainly be in any report I would ever see, and in this state, all of that would be public record.
This event is also a good example of why I advocate layers of defense - fencing, dogs and other alarms (10 seconds more notice might have made a hell of a difference), and generally more than one firearm. This is even more applicable when one has a bit more reason to fear real attacks than the average person. While I always have at least one handgun close by, and at night at least 2, the primary is an AR for darned good reasons.
This is also an example of why I don't care about spending more money to get good quality guns and gear, and to buy large amounts of quality ammo for testing and the like. (I almost never buy in quantities of less than a case, and often it's several cases at a time.) It's a priority that matters, unlike wasting money on silly stuff like going to movies and pro sports, owning a boat, etc. If one's risk level is high enough, as mine has been, the priorities simply have to be different. Of course, that does require accepting the possibility that such things can happen, and many people, including some on this forum, don't have the right mindset about that.