Obviously anon is a fucktard.

That being said, the situation isn't unrealistic. It's always amazing how people can misread eye movements.

So, if I'm in that kind of situation, my first thought is to look around and behind me. Could be there's something nearby that's drawing attention. You know the trope of seeing someone waving and just automatically reacting like they're waving at you, even if you don't recognize them?

It's the same kind of response. We're semi trained, and semi instinctually driven to respond to established social cues in kind. Someone waves, you wave back. Someone extends a hand for a shake, you respond with your own hand, sometimes even when you don't usually shake hands.

Anon there could just be misreading a cue that isn't directed at them.

Or, and this is more likely, anon sees pretty lady, and is glancing at them frequently. This can happen without really being aware that you're doing it, our eyes tend to move around without conscious intent a lot more than people realize. Pretty lady is reacting to anon's glances.

And that's ignoring any of the tiny movements we make without paying attention that can draw the eye. You rarely think about something like adjusting your posture when you're focused on something. You move, pretty lady catches movement, her eyes and head move, you catch that motion and glance towards them.

We all engage in little dances like that, often without ever realizing it's happening. Minor shifts of body and head as two people share space that are essentially meaningless, but mimic things that do have meaning.

Depending on the kind of work involved, it can get very complex, and still be utterly unconscious.