I'll defer to you as you're definitely more familiar with the rule than me, but i'd be interested in hearing from refs (or other refs, if you're one), I know a few others are on here.
But I still don't think Poulin's leg is "blocking" Ungar's, I think his hip is doing all the work; and yeah, his hip does that work a split second before it's grounded, but the fact that it's his hip and not his leg or ankle, to me, means that he's delivering Ungar to the mat safely. But I also totally get why, even if my distinction was meaningful and I'll buy your explanation that it's not, refs should just blow the whistle.