Many of the other extreme elimination diets I tried showed obvious signs of micronutrient deficiency. For example, I tried bread and water, lean meat and water, etc. It's easy to recognize signs of deficiency - fatigue, cravings, etc.
But I wouldn't say scallops have everything. I did lose weight. I think you'd have to add in some fish to get a complete diet. Not so much for vitamins or minerals, but for something related to satiety and macronutrient composition. It could be insufficient fats/oils, or maybe you can't get enough protein because it triggers satiety too fast due to impending overdose of some micronutrient. Or maybe it's just the taste.
I've been going for many months on a diet of solely rice, fish, scallops, rice and shrimp. Since I'm still healthy and productive, there can't be any short or medium-term deficiency there.
In general, however, a meat-only elimination diet works. See the Stefansson trial, and his study from living with Eskimos. Meat with sufficient fat on it is all that is needed to sustain human life, and it can even come from a single animal, as long as that animal isn't being grain fed from mineral depleted soil.
Thus it's not so much surprising that rice, water, and any X meat is sufficient for health. Rather, the extreme positive biological reaction to micronutrient overload from high scallops intake is what's surprising.
Why do you think it is that supplements are so much more toxic than food? Eat a dozen oysters, you'll get 1200% of the RDA of zinc and feel great. Eat 12 zinc pills, and you'll probably vomit within 5 minutes.
What about food buffers the effects of minerals? I've come to understand that the ratios of minerals is of supreme importance and of course food has much more complex ratios of minerals, but I'm sure there is something else going on here.