Mayonnaise is safe because the acidity is sufficiently high that the pathogenic bacteria we're worried about can't grow.

A 100 day experiment isn't very long. The figures I've heard for salmonella % in chicken is on the order of 0.1% Good chance he never even encountered it.

Also depending on where you are, producers are required to vaccinate their chickens against salmonella. That makes raw chicken even safer to eat. Similar measures in North America for pigs have made undercooked, and even raw, pork pretty safe to eat; it didn't used to be.