When is a wall not a wall?

In the New Yorker we get the following paragraph:

In 2005, Banksy travelled to the West Bank, where he painted the security fence at Bethlehem with a trompe-l’oeil scene of a hole in the concrete barrier, revealing a glittering beach on the other side; it looked as if someone had dug through to paradise.

The article contains a photo and caption as well.
A Banksy trompe-l’oeil painting on a security fence in the West Bank.

Strange that the painting in the photo seems to be on a big motherfucking wall, while the fence in front of it is paint free. I wonder if they got the wrong painting.