Possibly it was actually human flesh.
Soylent Green is people....
That would make sense. Used to be grave robbers would swoop in after the funeral, dig up the corpse and give it to doctors and medical schools to jab around in. Now they could do the same exact thing, and nobody would be the wiser, and some who might find out would decide it’s a good thing. And those who wouldn’t like it, would pretend they don’t know, like Sgt. Schultz.
Or, they could figure out how to spice up some soy crap to taste like human flesh, I suppose with a sampling of corpses to make the comparison with.
The whole idea gets increasingly creepy.