I read about this theory as well. So, I decided to do some digging on Arian Foster and the conspiracy itself and found some information about the podcastt.
I found multiple articles (like the one I provided below) that states that NFL players, including Arian Foster, have been joking about this theory on Twitter as a sort of trend. An article by Bridget Reilly on the New York Post started, “ Following the release of the clip on Twitter, many users, including professional players, ran with it, using GIFs, videos and more to poke fun at receiving their ‘scripts’ for certain happenings in their careers.” So, as far as this information goes, I believe that Arain Foster was not being serious with his answer.
Now as far as the theory itself, yahoo news covers an interview with Patrick Mahomes about the theory and he stated that it was not rigged because the NFL does not care about a team winning or losing.
https://nypost.com/2023/02/02/arian-foster-causes-stir-after-joking-the-nfl-is-rigged/amp/
https://news.yahoo.com/no-nfl-isn-t-rigged-153637677.html