He's an incompetent clown, the tiles have not been set out correctly, the edges should have a uniform width.
To set tiles you find the centre of the floor and the decide whether the tile edge or centre should be on the centre line, this is decided by the edge cuts which should be as large as possible. Then do the same in the other direction.
No point explaining this to your bloke, his brain will explode. I wouldn't bother threatening him in any way and trying to sue him will be futile.
Reality, let him finish, could be when its finally grouted it will look acceptable