To me it's just another example of what people overlook or allow in sports figures they don't in real life. I actually don't recall hearing this and with someone as famous as Peyton that's pretty remarkable.
And the Manning's violating the NDA to talk about her is pretty common.
People remember the Oregon case a few years ago where 3 players were charged with sexual assault. Basketball, one of them had a very similar charge at his prior school which Oregon's coaches were completely aware of when they took the kid as a transfer. The players denied it, the school let them continue to play, but then after the season all 3 were essentially forced to transfer when the girl pushed for and a Title 9 case was filed.
oregon settled out of court for 800K and lots of people said see, she wanted money that was it. The reality was that Oregon explicitly removed the players from the case, the deal was that she got the money and in exchange Oregon didn't have to admit to any wrongdoing by the coaches or AD or school to try and help their Title 9 case. Why? Because it came out that Oregon had violated the law and leaked her personal information and medical information during the investigation, a complete violation of her rights. Oregon has never explained how that happened, they just apologized for it and paid the 800 K plus a free college education for her.
If those 3 players were just regular students, they would have faced charges, in this case no charges were filed and they got to transfer to another school, again on scholarship.
Given how big Peyton Manning was in college should not surprise me at all if he did that he was able to get away with it.