I actually wouldn't be surprised at all if this is true. LeBron James has been shown to be a bit of a punk, at least on camera, in front of his coaches since joining the Cleveland Cavaliers. Whether it was David Blatt or Tyronn Lue, James seems to act like he's actual head coach.
It makes sense why Blatt got fired, since James never showed much respect for him. Blatt never really challenged the King, and it looks like Lue took note and took the matters into his own hands.