SAR is a technique for building up a two dimensional image by rasterizing one dimensional signal reflection data. Any type of radiant energy would presumably support SAR techniques, from sonar to x rays, although the 'R' in SAR presumably limits it to radio frequency range (~30Hz-300GHz). Some of which, as I mentioned originally, absolutely would see through buildings.

My point is that the headline and article are trying to make the case that 'SAR can't see through buildings', when it should be 'Why it looks like our satellites are seeing through buildings' because that is all that is explained.