Consider this another vote for the Judeo-Christian view of "meat" contributing to the confusion, even in modern culture. I grew up right outside of a very Irish-Catholic section of town, and Fridays were all about fish (and more specifically, "not meat"). I grew up well after Vatican II, so we only really followed it during Lent, but it was so ingrained in the culture that many had fish-Fridays year around (with the admonition "don't eat meat; it's Friday"). However, I grew up in a family that couldn't stand fish so Lenten Fridays were all about Lasagna and other pasta dishes for us (again, all falling under the "not meat" category).

But yeah, all of my relatives/childhood friends were Eastern-European/Irish/Italian-Catholics, so "fish" and "meat" were two totally different things.

Thanks to me, though, my brother and husband refer to pescetarians as "fake Vegetarians." I train them well  8)

PS--I remember a seventh-grade video in geography class of Russian fisherman harvesting roe from the bellies of fish was one of the things that helped me turn vegetarian... yuck! (The Catholic hypocrisy of eat-fish-not-meat was another one.)