You're likely not getting lamb for $25, plus I'm looking at the stitching and the palms where the creases are. It doesn't look like calf, so I would guess pig skin. 100% (or genuine) leather is actually a grade of leather. It's one of the lowest grades. But even pigskin will last a long time. I have a trenchcoat that is 25 years old in pigskin, and it looks brand new through every single winter. I usually I have to maintain it near the end of the season before it gets put away, but it's been great.

Disclaimer: I have owned a LOT (like a shit ton) of leather items (specifically gloves, shoes and coats) over the years, but I could be completely wrong. Costco has often had some great deals and a $25 pair of lamb leather gloves is not completely out of the realm of possibility.