The woman just gave birth. I'd give her a pass and let it go.
I remember whooshing off 30-40 ish lbs with the birth of my kid. There was her weight (9lb+ was just HER!), the weight of the placenta and cord, the swelling and serious mega bloat I suffered from all thru her pregnancy, etc.
Like you, I doubt it is fat loss.
But I'm inclined to be charitable and just say "That's cool." and let it be.
A.