Despite Perreault turning up ice, Armstrong certainly came at him from a straight-ahead direction. You can see video of the hit here.
That does not change the fact, however, that Armstrong’s hit was dangerous and highly illegal. This is not a case of Perreault skating with his head down and then getting rocked, but of Armstrong needlessly leading with his hand and forearm for what should have been a big open-ice hit.
Perreault attempted to dodge the hit at the very last instant, which contributed to the hit looking pretty bad. That doesn’t change the fact that Armstrong’s hit was illegal and he should face supplemental discipline for the hit.
If the league has to be ruthless with punishments to get players to stop being foolish, then so be it.
Update: Here’s the video of the hit from NHL.com.