JP, here is my understanding of the play and how it applies to the chop block rule.
The mike was the guy they blocked. Only one was supposed to block him, but two did as there was some confusion about who was going to block the mike.
It’s okay for both to block him at the same time, But, according to the rule they must both block above the waste.
On the play one UT player went low and “cut” the defender by hitting him below the waste. That’s a legal block as long as another blocker doesn’t engage the defender above the waste which he did. Hence, the reason the chop block was called.
Essentially, there cannot be one player blocking the defender above the waist while another blocks below the waist.
I hope this helps.