Possible that was the outcome of the contact...
To think Harper jumped in the air looking 'only' to grab Bulas arm is a bit far fetched
(Especially since it's Harper)
Went up with an arm up at a chance something would come of it... And made contact no doubt.
Harper also following the ball from the underneath, Much less chance of getting close.
I saw nothing in it, certainly not a penalty.
If the exact situation was reversed here - I have little to no doubt there'd be as many arguments the other way....
In fact - If I cared to, I could probably find some from previous games...