You don’t understand the rule.If you watch it in real time, he is going full speed, trucks our RB and is stumbling toward Mac. He did not dive at Mac's legs. He was falling down as he grabbed Mac low. He literally just wrapped him up. Did not twist him or spear him or anything.
By rule if the only place you can hit the qb is low, you can’t hit the qb.
The only exception id if someone blocks you and forces you into the hit and you have no way to avoid it.
It doesn’t require diving, twisting, spearing or anything.
By the rule, Roberts responsibility is to not make contact because the only way he can is hit low.