No, I think accidental head clashes are relevant.
They are dealt with under the law application guidelines e.g. some of the examples here:
https://www.world.rugby/the-game/laws/guidelines/17
If Swinton had wrapped his right arm and made a legal tackle and then the two had clashed heads I don't think it is foul play at all and no card or penalty should ensure.
If Swinton had made a no arms tackle that had started below the head and then it was the shoulder that slipped up into Vermuelen's head with significant contact it would have been a red card in my view because that isn't sufficient mitigation.
The fact that it was a head clash is relevant.
It seems to me that the Laws only talk about accidental contact in determining whether the head contact happened due to ‘foul play’. It then talks about what is considered ‘accidental’
‘Accidental contact with the ball-carrier tackled into the defender’
‘Friendly fire’ as the two defenders clash heads
‘Absolutely accidental head clash between white 15 and red 14 - both competing for the ball at the same height’
It seems that there is no consideration for ‘accidental’ if you are actually in the act of making a tackle. Basically you intentionally went into contact and so any contact to the head is not considered ‘accidental’
So if you follow the guidelines for the Swinton tackle:
Was there head contact? - Yes
Was there foul play? (not accidental as per above) - Yes
Was the danger high? Yes
Sanction - Red Card
Mitigating Factor - Head contact was secondary
Sanction - downgraded to Yellow Card.
Going by the same guidelines, Weiss should have received a Red Card as there were no real
mitigating factors. This is probably what the citing commissioner has seen.