Wow, that's a bizarre one. I've been to a stack of sales in Australia, New Zealand and North America ... but I've never seen that one before. Some weird hock stability test or something. Sounds like total rubbish to me.
I usually just pick up their feet, watch them walk, do the standard stuff ... nothing above that. I think after a a bit of time you can work out if you fundamentally like the look of a horse or not almost straight away - then it's a matter of checking a few specifics like joints, structure, etc.
Maybe the old tail-grabbing rump rockers are geniuses - and we're the crazy ones!!