One's a "just replace the timing belt" thing and one's a "actually set the timing" thing.
If your timing is perfect.... cam is exactly in the right spot at TDC etc and all you need to do is put a new belt on then you quite often will not have to loosen the camshaft sprocket... the new belt may just slide into place and not move when you tension it.
If you want to replace the belt *and* make sure you have perfect timing then you go for the full-meal-deal proceedure... Engine at TDC, lock the cam and pump, break the cam sprocket free, install the belt, tension, tighten the cam sprocket, remove the locks, set the pump timing with the dial gauge.
So, both instructions are correct, just talking about slight different things.
Vince