AirRabbit, thank you for your courteous reply. It helps a bit, but I still don't quite see what he was trying to achieve by this.
I don't fly (in my next life!), but I do sail small boats, so for me it's as if he'd put the tiller hard over and then, just as the bows started to swing, slammed the tiller hard over to the other extreme. And then repeated this 4 more times.
This won't get you anywhere in a small boat and I can't imagine a situation when one might do this, even in a blow and a running sea. I know aircraft are not the same as small boats but it still sounds rather odd.
I'm sorry if it's a silly analogy but I'm trying to understand.
PS: On reflection, you might well break the rudder off in a dinghy if you tried this, so what happened is not that surprising. But why do it?