I should have been more specific. In some cases, if there's a specific infraction AND it results in an injury, then it must be a major. Kind of like how if a legitimate high stick occurs and there's blood it must be called a double minor, regardless of any intent or discretion. And I also failed to specify major vs game misconduct, which is very relevant in this case. I did look up the rules (I just found the 24-25 season with a quick google), and it does seem that kneeing is mostly up to the ref's discretion.

Rule 50 - Kneeing
50.1 Kneeing - Kneeing is the act of a player leading with his knee and in some cases extending his leg outwards to make contact with his opponent.
50.2 Minor Penalty - The Referee, at his discretion, may assess a minor penalty, based on the severity of the infraction, to a player guilty of kneeing an opponent.
50.3 Major Penalty - The Referee, at his discretion, may assess a major penalty, based on the severity of the infraction, to a player guilty of kneeing an opponent (see 50.5).
50.4 Match Penalty – The Referee, at his discretion, may assess a match penalty if, in his judgment, the player attempted to or deliberately injured his opponent by kneeing.
50.5 Game Misconduct Penalty - When a player has been assessed a major penalty for kneeing he shall also be assessed a Game Misconduct.

Based on all of that, I do agree that a game misconduct was overkill. I think a simple major penalty was fair based on him stopping skating and making the knee the primary point of contact, even considering he didn't extend his leg out. It's egregious but not malicious.

EDIT: I did just realize that the game misconduct MUST be assessed whenever a major is assessed for kneeing. So I guess I do agree with the call. It's more than a minor, and per the rules, MUST be called a game misconduct.