This video was before patch v22.214.171.124, which adjusted the taunt and damage radius of his ult. Before the patch, the taunt radius was larger than the damage radius, so it was possible to be taunted, and not damaged. Patch notes below:
Originally Posted by Udyr
Idol of Durand
Taunt radius reduced to 500 from 520.
Damage radius increased to 520 from 500.
Adjusted team colored range circle to more accurately represent taunt range
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You can see the taunt animation on him... That's the thing.
When they move out, it doesn't entirely pull them back in.. resulting in no damage being done.
If it's going to taunt them it should pull them back in..