They started correctly bottom left (pic 2) but then found they needed to add more addy on top of the ribs of addy to keep the tiled surface flat, so then they gave up with the notched trowel. Look at the thickness of the dabs on the wall - if the front of the tiling was flat then the wall definitely isn't. Many, many years ago i'd have done the same (but with more dobs so that they all touched each other when compressed). More recently if the wall was so far out it would be coated with the notched trowel and then more addy would have had to be added to the already back buttered tile to keep the tiled surface flat over the hollows in the wall (I know against BS5385), either that or i'd loose a day (unpaid again) and do the plasterers job for them!
Were the tiles fixed onto the notched trowel bed more difficult to remove than those dot and dabbed? often I find those dot and dabbed are harder to remove.
Crumbs I've just relooked at the pics - one wall is so bad the tiler had to fix tiles in the hollow and then tile over them. I'd definitely would have had to flatten out that one!!! Hope that's allowed for in the retiling price.