yea it's correct, 16-bit signed is −32,768 through 32,767 while 24-bit signed is −8,388,608 to 8,388,607
"steps" is not the best word, "values" is better... and I wouldn't say "stair steps"... I did come close but yea it's a "bit" misleading
love that video btw, saw it years ago so it was a nice refresher. noise floor improves as he clearly demonstrates, but so does that quantization error (or jiggly movement in the waveform) of course you can't hear it in most cases, but he doesn't go into how that effect can become exaggerated at lower gain settings... there's probably a better video that demonstrates that out there