So do you think NB got confused, and thought the BC was the Arg player at the back of the maul, rather than the SH... and that the Eng player was bound on the whole time, making it a same-maul situation?
If so, that should be scrum Eng, because Arg took the ball in to the maul which became unplayable (and it was from a line-out, not kick in open play.)
If it's not a same-maul situation it's a clear PK to Arg for not releasing/not rolling away.
I can't come up with any scenario in which it's scrum Arg, even if they were "the team in possession".
I agree with your comments, though I am also unsure about the player in the maul being onside and allowed to tackle the 9.
I also expected a penalty for Eng not rolling away, because the Eng player clearly fell on the wrong side of the tackle... if not a penalty, then it should have been an Eng scrum because Eng were the team last moving forward.
Futhermore, there was another occasion (I can't remember which game) during the knock-out games that the same thing happened but the player in the maul was penalised for changing his bind in the maul, however, he was bound in the maul (not on the side), therefore it was my understanding that you can freely move your arms.
Going back to my uncertainty about a player in the maul playing the SH, I raised this in my Society WhatsApp group, but didn't get a satisfactory answer...
Clarification 3-2021 confirms that a player in the ruck remains offside when the ball is removed and cannot immediately play the scrum half. My Society colleagues were of the opinion that this clarification does not apply to a maul, and that a player "cannot be offside if bound into or on to a maul".
However, coming back to
Clarification 3-2021, WR stated that "If a player is fully bound and they have moved beyond the offside line then they must return to be behind the hindmost foot before being able to be involved in play, once the ball is out or is played from the ruck." After reading the law book, the only law I can find that directly aligns with this statement is law 10.9, which applies to a ruck, maul, scrum or lineout ("A player who is offside at a ruck, maul, scrum or lineout remains offside, even after the ruck, maul, scrum or lineout has ended.")