All depends on what narrative you want to focus on:
With the "PSU has only played one good team and they lost" narrative, the Wisconsin game was a tale of back-up QBs so it still shouldn't have been much of a challenge.
With the "PSU has shown it can overcome adversity" narrative, the Wisconsin game counts, along with the USC and Minnesota games (even though these could be called 'self-inflicted adversity').
All these narratives show that (1) we really don't have a good way of comparing teams from different conferences; and (2) with the 16+ team conferences and uneven conference schedules, it's getting harder to compare teams within a conference. Also, teams are not static; some improve during the season and some get dispirited and decline, so even comparing common opponents is problematic.
That is why a 12-team playoff is a good thing. We will find out who has the right stuff, as the champion will have to beat 3 (or 4) ranked teams in a row in order to win it all.