Perhaps a better approach would be to attack the dimensions of the boat itself, as well as the materials used to make it. They could still cry “magic!” if they wanted to, but it’s a bit sillier saying that the boat was a specific size but somehow still fit all the millions of animals onto it (did “God” shrink them down to pocket size?). I mean, if that’s the case, when why build a large ship at all? They could have used a raft if the animals were going to be magically shrunk, or if size wasn’t an issue.