but the dull smooth green is confusing. Kombocha?

either a small regular one, or there is an heirloom called 'baby blue' hubbard. let the seeds dry and plant next year if you want

I am an heirloom seedsaver for the last 30 years
I used to sell them on localharvest.org

I believe it's a wild gourd. They're seen growing beside the roads often.

Maybe yellow?

...it appears to have a small flesh to seed ratio ...
... could well be a 'volunteer' of a previous season's hybrid species; which means it is a parent, and seldom best quality...
... unless you have ample space (all gourd family plants are garden hogs) I wouldn't plant the save seed of this...
... however, the seeds can be tasty when dried; and of course the flesh from this one is may have a good taste when roasted...

Got together and had some fun under the leaves. They cross pollinated, I had no idea the acorn squash seeds I saved from the fruit must have been contaminated with zucchini “DNA” .
Because this years seeds did really weird stuff…some are round Acorns squash no problem…some are zucchini with a slightly harder skin, if picked early it’s fine, if not inedible…but some of those are showing characteristics of an Acorn, albeit oblong…we”ll see.

I sliced open one of the squash’s and it looked similar to those pictures.