Well, I half agree here.

Assuming someone's physical appearance is such that they have a large belly. Assuming that they are pregnant (if true) is likely to make someone feel good, whereas assuming that they are fat (whether it's true or not) is likely not to make someone feel good.

It depends if there's a base assumption that someone is self-conscious and has a negative feeling about their size.

I certainly think it's reasonable to say that you implied someone was pregnant to make them feel good about themselves.