He asked me "Is it a fake or a real smile?" Why he asked me that?

Last night I posted a picture on instagram with my sister from going out. One guy replied to my story "😍". He followed me a few months ago.
He is the brother of a guy I was with for a couple of years. It ended badly. He now has a girlfriend. I haven't seen him in 6 months.
I send him "🤗". He replied "Is it a fake or a real smile?" I replied that it was honest.
I don' understand what he meant.
What that message meant?
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Did he mean the smile in my picture or the emoji "🤗" ?
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He was with his brother (with whom I was) that evening. They sat together. Is it possible for him to send me a message while he is next to him? Isn't he uncomfortable?
He asked me "Is it a fake or a real smile?" Why he asked me that?
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