Replacement Strip of Siding
With vinyl siding, you start at the bottom and work up, so when you get to the top, you're left with a piece that probably needs to be cut.  You try to measure before you start so you have close-to-a-full-piece at the top, which is what seems to be the case here.  I'm guessing you found a new piece in the garage that would need to be trimmed a little.

Look at how much the existing top piece seems to be cut, and how the top is fastened into place so you don't cut the new piece incorrectly.  You might be able to pull on the edge of the existing piece to get a better idea of how it's being held in place.