His becoming untargetable happens a little earlier than when he's actually on the pole, and lasts until after he's dealt the damage by jumping back down-- which means the tooltip is wrong.
The text says he leaps onto the pole and becomes untargetable. It doesn't say he's untargetable as he jumps-- and it doesn't make sense from a gameplay standpoint that he does.
Either the ability needs to be fixed so that he's only untargetable while actually up on the pole, or the text needs to read that he's untargetable for its entire duration. As it stands, he's just incorrectly immune to Taliyah's E and Poppy's W.