I'm surprised it hasn't been brought up: Those people might just be shy. When I was younger, some of my friends had problems keeping eye contact (both with guy

I'm surprised it hasn't been brought up: Those people might just be shy. When I was younger, some of my friends had problems keeping eye contact (both with guys and especially with women) and instead they were naturally inclined to look down or scan our surroundings. That was before everyone started carrying phones around, so maybe that "shyness" behavior has just shifted from looking down to looking down on your phone.