> it will let a function jump to another function ... isn't that what's essentially described here?

Not exactly, they're describing doing it without a jump - the first function simply ends at the start of the second function, so the CPU starts running the second function directly after the first with no jump necessary.

Edit: If you're saying a tail call could enable such an optimization, you're right, but it still requires placing the functions in the right spots to eliminate the jump entirely, which is hard.