That's kind of a trivial observation -- if chess AI were predictable to grand masters, then those GMs could play like the AI and thus wouldn't lose to it.

It's not predictable of course, but the parent commend said:

> surprising, even human super grandmasters can't always understand

Of course they don't expect the move, but they always understand it, even if it takes a bit. There's no move an engine makes where grandmasters go "I can't understand this", it may take them a bit, but they will always ultimately have a good idea of why it's the best move.