Please see this discussion about this question from a bit further down the page.

Dave

Here is a link that might be useful: Squash volunteer

"Is it possible for those two types of yellow squash to cross-pollinate? If so, then what would I call these?"

They have certainly cross-pollinated. You can call them whatever you like as long as the name isn't already taken. It's your own variety of squash. If you keep them from being pollinated by another variety and save the seeds, you can grow them again. Next year there's a possibility they will be even more variable but through careful breeding/selection and several years you might be able to stabilize the traits.

Rodney