Iran may be supplying some weapons, but their involvement is not comparable to the Saudi involvement. Even the arms supply is questionable. The missile attack is the only solid link given, and the proof provided does not say when the Houthis acquired the missiles or when they were used. The details are in the linked articles in your NYT piece.

The UN also tried to start an investigation into Suadi war crimes, but it was blocked by the UK. https://www.independent.co.uk/news/world/middle-east/boris-j...