I think humans are well adapted to a shoreline diet due to bottleneck event(s) caused by some natural catastrophe that rendered extinct those humans without access to shorelines.

I think you're overreaching the idea of adaptation there. Scallops and other bivalve molluscs contain a lot of dietary protein, and also a lot of nutrients we need; part of the reason we need many of those specific nutrients is that unlike even many of our closest relatives, we can't synthesize them internally. So it shouldn't be surprising that a food rich in those things, with very few "empty" calories and which is not too calorically dense would be beneficial...