Chibi Halo
Remember who Jack swiped his new pumpkin head from. Who's to say Peyo wasn't carving up a Diedrich themed jack-o-lantern for Halloween this year when Jack came upon him. He was wearing a Diedrich sweatshirt/sweater at the time. Jack's heads might not always look the same every time he uses them if they're not all carved the same. Then again those could be horns and his demonic side is starting to show through.
Yes, I remember Jack took the pumpkin from Peyo. However, there was no "bunny ears" or "horn" in the comic when Peyo was carving. So I really don't know if Jack carved that after stabbing himself in the face. Truth be told, I thought it was just a piece of the pumpkin that Jack carved himself.
Heck, if you look at the pumpkin Jack used in the comic and the picture Uncle Kenny posted, you can see that the stump is fully attached to the pumpkin, not being cut from the pumpkin. There was no line. So I don't know if Jack had switched another pumpkin after stealing it from Peyo or if that was the merging of EB with Jack after the bombing incident or Jack's power fused with EB.