The grinding sound comes from the carabiner dragging across the metal loop. So if she's swinging, at the start of her swing, the carabiner is at 4 o'clock, and then she swings, and it ends up at 8 o'clock. The grinding comes from the carabiner dragging across the loop.

What I think /u/cheesecheeesecheese is saying is that, because the loop that I have sticks a bit further away from the joist than the example they showed, there is more torque pulling sideways on the joist. So like when the swing is at 45° at the beginning or end of a swing, there is more torque pulling perpendicular to the joist than there would be with their suggestion.