That isn't true, but whatever.
There's a fairly wide range of reasons someone might be able to walk and still need the technique applied, and it's bullshit that this twat implies otherwise
Edit: I'm too pissed off to leave it at that.
Walking by itself does encourage lymph to move through the body, that's true. But it isn't the only way it happens, and more importantly it scales with the duration and intensity of the walking.
So, anyone with something like osteoarthritis in the hips and knees is going to be going slower and needing more stops, reducing the efficacy of walking for fluid movement.
Fibromyalgia is another big one that vastly limits walking, and directly benefits from the fluid release massage along with the lymphatic movement it promotes.
It really doesn't fucking matter why a person has limited mobility though. This asshat and his smug, ableist bullshit can go fuck himself. Just go for a fucking walk. Jesus fucking Christ, what empty headed drek comes out of people