I think the discretionary portion of the call in this instance is whether Marchand would have broken free before getting too close to the crease or not. With the little separation he had when the penalty occured, it’s not a penalty shot unless it’s clear he would’ve broken free if not for the slash/hook/hold.
I think he would have in this instance, but the ref probably didn’t. We scored anyway, and while Marchand is great on penalty shots (not shootouts), I’ll take that 100% hindsight over a penalty shot, even though the Rangers were perfect on the PK in December up to that point.