Sorry to burst your bubble, but it was too good to be true. I guess if you think about it like that OP does appear to be a misnomer. OP just means that you can save seeds and expect them to be identical to the parent IF they aren't cross pollinated. You need to hand pollinate if you want to save seed.

When I think of OP I think about how the seeds are collected commercially. Chances are OP seeds are grow in one large patch of nothing but that one variety. And it is planted far enough away from related species that you can be nearly certain there was not cross pollination. Hybrids on the other hand are the result of some worker selecting the parents in most cases.

You still don't absolutely have to hand pollinate if you don't want to. Chances are you will end up with something very similar even if cross pollination does occur. But if you want to be certain your seeds are pure, then you need to hand pollinate.

Thanks. I thought it was something like that, and thinking about it now, that makes perfect sense. Territorial also sells some F1 hybrid winter squashes, and I guess the difference there is that you can't save seed at all.
No problem, my bubble is not too badly burst. I'll just hand pollinate carefully. Although I think I'll use ziploc sandwich bags instead of masking tape. And I'll never have to buy winter squash seed again.