There was a comparative relationship there that the number of shrimp has gone down, but the total weight of shrimp has not gone down. If we think about the math involved, your total weight of shrimp is just how many shrimp you ate times the average weight per shrimp. If I eat 10 shrimp and on average, they each weigh about 20 grams, and I eat 200 grams of shrimp. If we find out that he's eating the same total weight or at least as much, even though the number of shrimp has gone down, then the only way to balance out that math is to infer that the average weight per shrimp has gone up. The possible inference these facts allowed us to make are that for the past two weeks, he's been eating on average heavier shrimp. B contradicts that idea and says that the shrimp he was eating a month ago are heavier than the shrimp he's eating now.