Passer rating is based on 4 separate categories involving completion %, TDs, YPA, and INTs. Each of these categories has a 'cap' (77.5% completion percentage is 'perfect') and going above that cap does not make up for being below the cap in other categories, which he was. But, that 'bonus' completion percentage will help when factored into his overall passer rating for the season.

There was a really stark example of this on Thursday with Drew Brees - he had 4 TDs on 22 attempts, well above the 1 TD per 8.4 attempts 'cap', so his passer rating was only 111 because he was well below perfect in other categories. However, that game increased his season passer rating from 126 to 127.3.