Just because it's a libre phone, doesn't mean it's necessarily a linux phone. Or at least any more so than Android is a linux phone because it uses a heavily modified (almost unrecognizable) linux kernel.

There's nothing in the article that says they're just going to use a mainline linux kernel and throw a touch optimized version of some existing desktop on it (ubuntu touch, etc...)

Heck, they could be meaning that they're planning on making their own heavily modified kernel for their very own OS so as to skip all of the trouble that trying to make mainline linux into a handheld device has been so far. (similar to I believe how SailfishOS is doing it)