This is about the 16th time I have seen language just like this used to explain away this concern. I don't know if you realize, but this wording makes it sound like you can select some photos and leave others local. I can find no indication anywhere, including on my phone, that iCloud Photos is anything other than an All Or Nothing singular toggle in iCloud settings. If you have instructions to the contrary, I will be happy to stand corrected.

Seriously, everybody is wording it like this. "Photos you choose..." and similar.