Q.How did i get this squash?
I bought a Delicata squash last year at the grocery store. Saved the seeds, and planted them in the garden this year. This is a picture of what developed. How can this happen?
Another gardening site suggested that I got the seeds mixed up. No — these were the only seeds in my house. I took them out of the Delicata, dried them, put them in a jar for a year, and planted them this year. NO OTHER seeds were in the house.

Your original squash was a hybrid. 'Plants grown from hybrid seeds typically do not produce seeds that can be used to grow the same type of plants, and can even produce seeds that will not grow at all.'
Read more at Gardening Know How: Learn The Difference Between Non-Hybrid Seeds And Hybrid Seeds https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/non-hybrid-seeds-vs-hybrid-seeds.htm