I think had he hand balled to McKenna the Cats player to his right potentially could have turned and tackled him almost straight away.
What likely happened was McGrath held onto ball expecting to perhaps draw that man, who actually just kept running fwd and thus he just took the kick himself as Stewart broke into space.
It's that kind of quick thinking that will see McGrath excel in the midfield, definitely made the right decision. It's beyond frustrating seeing handballs go to players who aren't in better positions/end up getting tackled quickly.
But as was said above if it was Goddard or Zerrett also streaming past one wonders if he'd have done same thing. You'd like to think he would.