Maybe he's giving them an "out" to explain to their nutty base that they really forced Trump to put up a "fence" instead of a "wall". So he says it was all their idea and gets the win.
Yeah ... or maybe it’s a headfake by the WH to show that Trump is willing to compromise — that he will go with steel instead of concrete (although he planned for steel all along). LOL
One possibility is that the story could actually be correct and the WH is floating the story to mess with the dems.