8 Bit vs 16 bit

I am not a game dev here but have a few queries. I was recently playing a game called "The messenger" where you move from 8bit to 16bit when travelling through time. So whenever we are in future the graphics and the sound turned to 16 bit and in the present the graphics were 8bit.

Now my query is regarding the 8bit/16bit sound and graphics? What do they exactly mean?

I read about the canvas size when making a pixel art game tends to be 88/1616/3232/6464 which directly means the number of pixels in a sprite, so if there are more pixels we can have more detailed sprites and animations.

For music, I read that it represents the number of instrument choices that you have when creating music.

Do you consider these explanations to be correct?