And there's probably many out there who eat big dinners and drink wine every day who are still skinnier than you.
They are skinnier than me because ...
1) They actually do eat less than me despite appearances to the contrary.
2) They exercise more than me.
Neither of those options would be hard to believe because I have a fairly large appetite ... and I'm sure there are lots of people who exercise more than I do.
They are not skinnier than me because of genetics, bone size, metabolism, muscle mass vs. fat mass, mysterious chemicals, global warming, global cooling, or any other excuses people might dredge up to lay fault on anyone or anything other than themselves.