Teemo and executioners calling?

So was going against a swain, first back, i had 1k gold, and he was about to turn 6, so I thought why not get executioners calling, since my Q was hitting for a lot anyway. Swain hits 6 and uses his ult, I start basic attacking him, and the calling doesn't go off. Is this a bug or intentional? Because to me, Teemo is doing both physical and magic when he uses his basic attack, but it's not proc'ing.