Not at all. The shower is beautiful and genius use of materials.

It is centered in the shower floor so pick your poison. Center on whole wall or in shower floor. In my opinion it would look strange to not have it centered in the floor.

Where did you get this tile that looks like shiplap?

This is not my project, but from the comments in looks like they used a product cut to size. I would likely use ceramic tile like this: Bright White Ice Ceramic Wall Tile - 6in. x 18in. - 100230788 | Floor and Decor https://www.flooranddecor.com/tile-decoratives/bright-white-ice-ceramic-wall-tile-100230788.html with white grout on the vertical joints and darker grout on the horizontal. You would just need to make sure you had a shiplap siding with 6" exposure to run into it.

My understanding is the shiplap look in the shower was created by using slabs of Corian. Very clever.

Ooo that is clever and beautiful.

Drain placement can be contingent on floor joist location, i think the offset is difficult to notice in such a lovely shower!

Even loving the "step up" trim into the shower how it ties into the shiplap look! Well done.

What is vendor for the plank tile on the shower walls?

Love

It's not plank tile. It's Corian cut into planks. Very clever.

Neither is off center.