In my experience cats patrol a large area which they consider theirs. But they almost always return at feeding time. If they don’t who’s to say if the cat was stolen or strayed. When growing up we had quite a few and none of them ever missed more than one or two days. Even the barn cats kept regular mealtimes so I find the stray theory for a cat that was a pet farfetched.
Enough of them are pets that it is normal for the shelters to scan them for chips.
So yes, cats do stray and people do find them and take them in.