It isn’t some black and white call like an obvious face mask or something. If a DB jumps up and intercepts a ball and the WR runs into them that isn’t DPI. If the DB runs through the back of the WR and prevents them from attempting a catch, that is DPI.
So in this case it’s a ref judgement call on whether the DB has position and the WR is running back into him, or if the DB is running through the back of the WR. In my head it’s too close to call and no penalty, especially considering the game context. KC always just seems to get the benefit of the doubt.