1. 30-40 stops in 20 matches says that he had 1.75-2 stops a match - which isn't very high.
2. In real life - that can go up to 3-5 saves in a match , and it wouldn't seem to be highly unusual , you'll just say "the keeper was good today" .
3. of course the GK of a weaker opponent will make more save than (your) successful team GK.
your opponents get 4-6 shots-on-goal so he has 1-2 saves , but their GK has a crappy team - so he'll face 9-15 shots-on-goal and if he had a decent day , he'll stop only 1-2. and saves 3-4 on a great day.
My GK this year has made more saves then i had with GK in previous year, And yesterday he saved 4 shots, my defence is great so it can't be that it is just because my opponents shot more -
so i started thinking "what's changed?" - the answer: my GK is young. which made me develop a theory:
He's young - young means he's not experienced :
If you're an experienced GK you let some shots fly-by because you know they're not really endangering the goal (that's why sometimes a goal gets in and the keeper didn't move) ,
as a young player - you save it instead of letting it fly-by (and that's why sometimes younger keepers concede by their fault and also the opposition has more corners).
so maybe that's why he's less stable and saves more at the same time - so maybe nordeus have an algorithm for that as well (and as a football fan who's team signed a 18yrs old keeper - i see it in reality too)