You can listen to a podcast of Larry Merchant calling into the Mason & Ireland show. He said how he dealt with Mayweather was a counter punch, not a sucker punch.
http://espn.go.com/los-angeles/radio/archive?id=2682382
Mayweather was irate because he wasn't getting love from the crowd. Instead of credit for dismantling Ortiz, he suckered him into a cheap shot. He knew it, that's why he wouldn't answer Merchant's question; and obvious from the boos from the crowd.