I don't want to comment on the Moruya accident because I wasn't in the aeroplane at the time and therefore don't have the first clue what happened or why. I'm not going to sit here and armchair judge a fellow pilot. But the concept of pushing into ground effect when you realise you are undershooting on short final is valid under some circumstances.
The first of these videos illustrates a scenario like aroa is alluding to, where the aircraft is low and slow, running out of energy and falling short without any spare airspeed. The second shows a more exagerated situation with plenty of energy to spare which probably didn't result in any better overall glide performance from the starting point, but it does illustrate just how dramatic the reduction in induced drag is.
It's not about being "better" than best glide speed. Overall, it isn't. The gain comes from the fact that in the initial pushover, the wing is unloaded with next to no induced drag for a few seconds, which gives you a small boost in momentum. Since the transition into ground effect from this pushover at this late stage in the approach takes only a few seconds, the higher parasite drag from the dive above best glide speed affacts you for only a small portion of the total remaining flight time and hence you get a net gain. It's not something to use as a standard approach plan, but it can be a useful dirty trick that you can pull if you realise that you're falling short and have nothing else left that you can do. The effect is more pronounced with high aspect ratio wings (e.g. gliders) but it works to an extent on any aircraft, more so if the prop is stationary (or at least, in coarse pitch) and not windmilling. Whether it's enough to be worth while depends on the specific aircraft type and configuration.
But again, I don't think it is all that helpful to speculate on why the guys in the 210 didn't make the field. Sometimes, sh!t happens. I'm pretty sure they didn't crash themselves into a tree for our entertainment, and in any case there could have been (and probably were) any number of distractions going on that we don't know about. Real world emergencies have a way of being a bit more full-on than the nice neat canned practice forced landing scenarios that most people base their supposed expertise on. So here's to just wishing them well for a swift recovery.