Any seedling squash/melon/cucumber plant is a mystery. For it to already have colored flesh means it might not be a melon, they take a long time to ripen, and they have highly lobed leaves. I just pulled one ten-footer out that probably sprouted from bird feed--it wasn't producing anything.

Pumpkins start out green, turn color in late summer. Try cooking one now and baking one in the Fall and see if it is any good. You might have some bonus food.

I too had an unusual squash that I have never seen before. It came from a bunch of buttercup squash seeds I planted, either from a collected seed or from a supplier. In any event, its egg shaped, with a gray skin, and looks nothing like a buttercup. Its bigger than a basketball in its larger end. I have saved its seeds and will try to grow some more this year. If it works, I might have stumbled onto a new strain of hard orange fleshed squash.