If you wave at a girl and she waves back and smiles but looks away afterward, is that a sign she is just being polite and isn't interested?

I saw her at the cafe at work and ran in real quick to get to the vending machine, and she was facing near my direction, waiting for her food to heat up so on my way back outside, I had to walk passed her so I quickly waved my hand up, and she looked at me and half smiled and quickly waved her hand up and down and looked away quick and still had a slight smile when she looked away. Is that a sign that a person doesn't want you to interact with them? If she were interested, wouldn't she have held eye contact longer? Was that a way of her being nice but letting me no know she's not interested?

If you wave at a girl and she waves back and smiles but looks away afterward, is that a sign she is just being polite and isn't interested?
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