Sorry, wanted to edit the post below but can’t! I meant to say, most of us do tend to equate fat with negative things, when we’re talking about ourselves. Even if we’re trying to become more body-positive, and even if we understand that society’s messages are BS, the inundation of those messages is hard to fight, and many people just can’t manage to get past it when thinking about themselves. So if you’re one of those people, it’s logical to assume that those you love will also be thinking/feeling something similar when they call themselves fat.
Hope that makes things clearer.