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?