I get the need to have a distinction between fish flesh and other meats such as beef, pork, and chicken, but using the same logic as in this article, I've always thought of fish as part of the general "meat" category. It confuses me how Catholics do the "no meat, yes fish" thing. Maybe there's some etymological explanation for why our current-day definition of meat doesn't explicitly have this distinction (assuming it ever did), but if there is, that context seems to have been lost long ago. For some reason, many people now just reflexively believe that fish is not meat -- even non-Catholics.

When I was a vegetarian I ran into people who thought meat was only beef… so they thought being a vegetarian meant sure, you’d eat pork, lamb, fish, chicken, turkey, just not beef. Kid of a weird thing to think, since for one a chicken is clearly not a vegetable, but also why even bother to make that distinction? “I have a special diet where I don’t eat beef!” and that sounds drastic to them. Some people’s minds are blown by the idea of no animal parts at all, like “What do you eat?”