What Ahsoka said – the Force resides in all living beings – is more akin to Empire Strikes Back Yoda’s statements. Some people naturally have more ability to access it than others.

The implication of what Huyang says is that no one would have bothered taking Sabine to the Jedi Temple to begin training. She has minimal natural ability with the Force. Ahsoka, in a way, is working with what she has.

Perhaps it was because Sabine inherited Ezra’s saber, so that’s why Ahsoka began her training. She has a light saber, may as well teach her how to use it properly.