Why was this posted? I don't think there's anything wrong with this question.

Because it's a classic flamewar topic which leads away from the specifics of this story and towards generic hostilities; and because taking a stronger interpretation of the comment would have made the question unnecessary—i.e. scott_s is probably just as aware as the rest of us that fish are animals and their flesh is in that sense meat, and therefore he was probably just not using the word 'meat' in that sense.

scott_s replied in an evenhanded way, but many (maybe most) commenters in his position would have taken the question as hostile and responded in kind.

How could I better ask the question? I'm genuinely confused since they poster talks about not eating "meat" but eats fish, which culturally for me (Buddhist and Hindu) are non-veg

I don't think the poster ever actually said that fish isn't meat, and I guess a lot of people are interpreting your question as a hostile challenge of the idea of pescatarianism (along the lines of "Why don't you think that cheeseburgers are murder?").

If you are struggling to understand pescatarianism as an idea, my perspective is that flexitarianism, pescatarianism, vegetarianism, and flexiveganism are all compromise diets that get some but not all environmental and ethical benefits of veganism. Different people have different levels of commitment and make different tradeoffs in their life choices. Whether that's "the only meat I eat is fish" or "I eat fish but not meat" is just a matter of definitions.

In terms of the English word "meat", there is certainly some ambiguity. At least as I know the term, it feels like a stretch (but maybe technically correct) to count fish as meat. I've had people suggest sushi when I say that I'm vegetarian, unaware that vegetarians don't eat fish. If you google for the Food Pyramid, most diagrams call out meat and fish as different things. "Vegetarian" almost always doesn't allow fish, but "meat" just isn't a very precise word.

Just adding the information contained in your second sentence here would have been enough to ask the question better. This kind of point is one that people typically get very hostile about, very quickly, in internet discussions, so if you're going to go there, you need to differentiate your comment from flamebait.

Also, scott_s's original comment didn't say that fish isn't meat, or even imply that. In English the word "meat" didn't traditionally include fish, and that usage is more than enough to cover what he probably meant. Taking the strongest plausible interpretation, as the guidelines request, makes the question unnecessary.