Guys what are reasons you’d give a girl a tight lipped smile?

So about two days ago I was walking by crush just as I walking by I got a funny text from my brother so of course I smiled looking down at my phone, and then on my way back I passed my crush again and I saw him looking at me and when I looked at him he gave me a tight lipped smile, he kinda looked upset? He usually stares a lot at me and gives me cute smiles. So I don't know why this time it was different.../: I hope I didn’t give him the impression I was texting a guy or something Iike that.
Guys what are reasons you’d give a girl a tight lipped smile?
Guys what are reasons you’d give a girl a tight lipped smile?
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