"Work is not always only about output and skills, especially in a small company run by 20-something whose only social life is their colleagues. It says nothing about your skills, just that both sides would probably be miserable in case you were hired, so it makes sense to find someone who would fit in the mold, even if less experienced/skillful."

Right, so better not hire any married people, older people, people of the opposite gender of the founders, people of the wrong political party, people of the wrong religious persuasion, the wrong class, or any other characteristics that risk interrupting the frat party...I mean "work environment".