Well then give me a real reason why it should not be possible. (Basically what they only say is why the appearance of penetrating building cannot be interpreted so easily)
Yes, they claim the 'laws of physics' prevent that. They should specify which law exactly. Maybe too low SNR? I know for a fact you can use radar to see through walls.
radar is a technique, not a specific thing. Their radar is based in the X-band (9.5 GHz) which is known not to have the ability to penetrate much. In fact, while C-band SAR (Sentinel 1) can partially penetrate forest canopies, and the top few cm of soil, X-band waves can hardly do this and basically just provide a surface scattering.
Well, thats splitting words a bit, isnt it? In that sense radio would be a technique not a thing (there is long wave, short wave, ukw, etc), or PCs (there is 8086, 80386,...) with some you can do run intensive algorithms in a specific time, with other you cant. Or what about cars?