Pre-screening developer candidates

> I want to know if they can communicate with me. I want to know if I can sit down and talk to them and enjoy myself. Do I get any weird vibes? Do they keep checking their phone? Can they talk with passion about their current work or work experience? If this doesn’t go well, maybe schedule a second one, or part ways.

Honest question, why do they think this sort of stuff is relevant? I've heard "can I spark a conversation with him if I met him at the check out line?" And other questions I can't wrap my head around.

Is it appropriate to meet for coffee to begin with? Is an ability to socialize well and "chat over coffee" important for roles that are not customer or client facing?

As a developer or engineer,do you find these skills relevant,critical or important to get your job done?