Can someone explain this (no mercy 2007)?

randy orton got awarded the wwe title and triple H challenged him and won and vince said since it was advertised umaga vs HHH that match would happen and the title would be on the line.then when HHH defnded mc mahon said orton had invoked his rematch clause and he fought HHH and beat him in a well earned win plus i have that PPV on DVD