Cortez was unclear and was at fault. Like you said, at one point he said lets go and clearly puts his hand between the fighters and removes his hand, signaling to the fighters that time is in and the fight is on. Then he looks towards the table as though he isnt sure if time is in. However, time was stopped with 9 seconds left in the round after the head butt and the ko was called at 2:59, so clearly, the clock people heard and saw Cortez say 'lets go' and started the clock. What Mayweather did wasnt illegal, but if he hadn't been head butted like that, he prob wouldnt have thrown those two punches. Regardless, he was dominating the fight anyway.