Tiling work in the bathroom - Is it allowed to do it this way?

No one will notice anyway except you during the first 2 weeks...

Without the description, I wouldn't have known what was wrong at all. :-D

I actually like it too.

Another question: What is the power outlet on the partition for?

Is she even allowed to be there?

Here the tiler has indeed thought something through, in my opinion. On the one hand, it is very symmetrical, and if he had done it as your plan suggests, you would have had a joint and a narrow tile again in the niche.
Furthermore, the tiles are arranged so that they fit perfectly into the room. Imagine if he had then tiled three tiles on the wall and had also laid them on the floor accordingly so that the joints would match again, you would now have a narrow strip under the sink.
That would immediately catch the eye when entering the bathroom and also looks unattractive. In this respect, I think everything was done correctly.
I tried to roughly illustrate how it would look if the tiles had been laid according to your idea.

I know what you mean, Theo.

I think the tiles look really nicely symmetrical and therefore harmonious.