Steffen got it for running more than half the length of the field to get in the refs face about the Aaronson situation.
First, there is no law against Steffen running that far from his goal area.
Second, it was a dead ball situation, so there isn't much of a focus on field players in terms of how far they roam from where they were before play was stopped. If Steffen were on the bench at the time of the incident, then that would be an issue.
Third, getting in the face of the ref would not by itself warrant a card. If it went on too long, that could warrant a card.
My suspicion is that the card was not based on how far Steffen ran to confront the ref, or his discussing/arguing the foul with the ref. Most cards issued in situations like that are given for dissent. And most cards given for dissent are based on what the player said to the ref (i.e., its degree of being inappropriate), with the second most common reason being persistent dissent by a particular player, which does not appear to be the case in this situation (though again, we don't know for sure).
I''ve rewatched the sequence several times, and I feel even more strongly than I did at the time of my prior post that the ref's actions caused him to miss the worst of the situation, and as such he really screwed up.