Not really. Anyone can have an "off" or "on" day. Happens in sports frequently where the underdog trounces the powerhouse.
If Riggs had really let himself go physically, it would have been even more likely that he would have had an "off" day.
I read the espn article, seems like intense training for the first match, drunken partying before the second match, something he supposedly never did while gearing up for a match.
I think he was sure that King would give him his promised rematch, but she refused. I bet a second match would have went very differently, and after the results of the first one would have made folks a lot of money.
Freegards