Who, exactly, is the goal expecter? It's Mike Dean, isn't it?
I've been looking at the basis for xG and while I can see some value in the broad scope (i.e. a whole season), it's useless for single games.
It's just another way of saying what we all see, just keeping better track of it over time. Once you start applying it to individual/few cases, you're totally missing the point of this kind of stat (and interpretative stats in general). But I guess it plays into the 'authority' role that the stats providers like Opta crave.
The last bit about Juve is on-point. i.e. xG is 'wrong' until enough games have been played.
Note that they never say who, what or how they decide? Just some broad explanation of what is a good or bad chance. It's Mike F. Dean. I swear to god.