It’s possible that he meant “Phat” and not “fat”. “Phat” is a compliment whereas the latter isn’t. BUT…I have NEVER heard the words “thunder thighs” used as a compliment or in a flattering sense. The “Phat/Fat” part might be ambiguous or unclear…but there’s no room for confusion (in my opinion) regarding the thunder thighs remark. That’s rude…and I think it’s best that she not waste her time on him and move on.
It’s even possible that he felt embarrassed about calling her “fat” and felt uncomfortable when she confronted him and tried to cover up for his mistake by saying “Oh no, I meant it as PHAT.” As I said above…“thunder thighs” is a more clearer indication that he’s not exactly being complimentary.
****** Maybe I’m more conservative…but I just think it’s unclassy for a guy to even outright make comments about a girl’s body parts during a first-time rishta meeting. That’s too forward for my taste. I can understand if a guy makes a broad comment such as “You look nice” or “You’re very pretty”…that’s more appropriate. Or if he wanted to be more specific…it could be a comment that’s generally more appropriate such as “You have nice eyes, etc”. Thunder thighs…? Nope, sorry. Tell her to move on to somebody who finds her attractive and conducts himself with class.