I was watching this video: https://youtu.be/W_dnYXJiTQU and got to wondering: what wood are quality Chinese boards made of? Is that kaya? The sound of the stones is very warm and soft. Another example: https://youtu.be/F7Jh5OnV6lo. I can’t imagine that these are just imported Japanese boards, because they have to be of different dimensions, right?

Video quality in both is not good enough for me to tell.

How about this: https://youtu.be/3O-lwNzN0G0 (and the whole series)?

I'm pretty sure that board is Shin-Kaya (it means "new kaya" but is a terrible misnomer, it's usually spruce of the Alaskan variety...not even the same species of tree [Kaya is a kind of nutmeg]). It'd be easier to say for sure if I saw the side grain and a better video, but that is probably what this board is.

Most one piece shin-kaya boards I've seen have a very clear, dark, strait, and width uniform grain whereas with Kaya it's subtle and not as uniform (except with the very best of boards, or composite pieces).

All the major outlets have shin-kaya boards for sell (Mr. Kuroki, Gogameguru, yellowmountain, yutopian and others).

If I don't have Kaya, I prefer Katsura but that's my own personal taste

Perhaps a euphemism for not-kaya or fake-kaya.

I don’t hear the sounds made on the board, but what’s the wood used here: https://www.youtube.com/watch?v=BZPQfGmpfn0 ?

I don't know, but it doesn't matter to me: I think it looks awful. From the video that is, perhaps it looks better in real life.
(as in bad; not like in awesome)
Sorry to say so.
Beautiful game though.