Rumours are that it was Tuchels side (Zahavi) who leaked the information to the media. Quite dirty if true.
Tbh, I think that Nagelsmann was mainly sacked bc of performance reasons. Since BL started again after the WC, Bayern is only 4th in the league. They had a 9 points advantage over Dortmund, now they are 1 behind. They achieved only 5 wins in the last 10 league games, that is quite shocking in Bayern terms. Also, 2 of their wins were VERY dodgy (VfB, Augsburg).
He clearly lost the dressing room like Tuchel did with us and they are performing very badly atm.