Ronaldo's lawyer is paid to make such statements so it doesn't come as a surprise.
However, regarding the settlement; it makes enormous sense why Ronaldo would pay it. It was weeks before his imminent departure to Real Madrid which he had been waiting on for over a year after reluctantly remaining at United for the 08/09 season out of respect for Sir Alex Ferguson who had begged him to stay the extra year. Therefore, if such an outrageous, morally in-dignifying allegation was to come out at that point: what he had been dreaming of his ENTIRE life would have immediately been in major jeopardy of not happening. As a result, it's probable that Ronaldo simply didn't want to take any chances so he paid her off to eliminate any small possibility of his dream move to Madrid being ruined as I very much doubt Madrid would have signed him if such serious allegations came out just before they secured his signature. Firstly, it would look bad on the club. Secondly, Florentino Perez already wanted to veto the move as it was sanctioned by the previous president so wasn't his own signing. It would have given him the perfect excuse since he only allowed the Ronaldo purchase to go through because of the boost it had to his popularity in the presidential elections for the club.
This is another reason why Perez so easily sold Ronaldo - he was never really fond of the player due to him not being his purchase.