Guy at work has no work reason to talk to me, sees me on the phone at lunch, what does it mean when he goes past if he stops, smiles & whispers hello?

We never chat but I like him, don't want to read more into a situation and get my hopes up.

Guy at work has no work reason to talk to me, sees me on the phone at lunch, what does it mean when he goes past if he stops, smiles & whispers hello?
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