The man you are interested in may squint his eyes and smile for all the reasons you have listed in your question or he may do this behavior because he thinks it is cute and endearing.
The eyes of children with albinism may move rapidly and not focus together, and the children may have to squint, tilt their heads, and hold reading materials close in order to see.
You do not want the sun shining directly in front or behind them, since this will create harsh shadows or cause people to squint when they're looking at the camera.
They frequently have poor visual acuity and are extremely sensitive to light (photophobia), which causes them to squint in ordinary light.
Well, two reasons: you won't squint as much and your eyes will be protected from skin-wrinkling UV rays (especially effective in the wraparound styles-and those styles fit over prescription eyewear).
Certain surfaces, like snow, water, and even windows can produce an annoying glare, the worst of which can make you squint, and even temporarily "blind" you.
She lifted her sunglasses to squint at him.
The glow of fire made him squint as they neared the field.
The sky was a deeper blue, the green of the spruce and pine even darker than usual against the incredible white blanket that reflected the sun so brightly one was forced to squint or wear sunglasses.
Gnaeus Pompeius, surnamed Strabo (squint-eyed), Roman statesman, father of the triumvir.