I’m an old legacy radar guy, mostly FME type so I’m not very familiar with Doppler radar. But I would think the greens, yellows, and reds are a function of target density that the Doppler computer calculates and then adds the corresponding color. I may be totally off on this, so please correct me if I am.
I don’t know either but that image sure looks like weather to me - that’s the way it looks on the radar we have on the flight deck. In my reading of WW2 spoofing stuff we were dumping long aluminum strips of the frequency the Germans used. We’re into millimeter or higher digital stuff and spoofing is pretty much all electronic now. I have some friends in the service and we chat about stuff and this came up. To me, it still looks like weather, and a target that large would certainly be noticed. Look at the area it covers.