I think that's a misrepresentation of the "view". It's not that they couldn't spear fish or catch birds, but that they wouldn't waste their time with fish and birds when big game was plentiful even if they lived near the coast. Just recently I watched a show that explained it exactly like that.

But I see a potential problem with that view anyway. This waste of time implies that fish or birds would not supply lots of meat, i.e. small fish small birds. I'd understand small birds, but not small fish. Fish today is very small but I remember watching archive films of fishermen catching fish with nets. The fish were tuna, gigantic 1000 lbs tuna. And they were plentiful. Then again, maybe big game was so plentiful and so easy to hunt in comparison that even if there was very large fish, they still wouldn't consider that worthwhile. That would make sense. Natural selection works when there is pressure like food scarcity, not when food is plentiful.