it would seem that one of his main issues is that he will have to redecorate the walls.
i cant see much problem with tiling although pictures do not show liping necessarily.
it looks as though your new finished
tile height is lower than original therefore necessitaing redecorating.
could this be what he is unhappy about and the adhesive/bonding above finished
tile height.
it will probably come down to what you have put in your quote or not.
if you have not specifically stated that he may need to redecorate walls if finished height lower than original as a result of not only making good walls before tiling or size of tiles chosen then he could interpret that you have not finished your works and he would be expecting you to make good.
it is actually not what i think he should be saying but it is an angle that he could put on you.
if you have not been very clear on what work you have quoted for and advised that by finishing at height you have done, there may be extra works required, i think you have left yourself a bit open.
this might cost you a little bit of money but may well save you a lot more in future.
if you can post your quote i think the answer will reveal itself.
dont give up on tiling.