what the bleep were you thinking ref?

so there i am watching mnf when i see one of the worst calls/rules i've ever seen.

the chargers were receiving a punt on their own 15 and signaled for a fair catch. the ball bounces off the returner's shoulder and goes up in the air in front of him. a steeler catches the ball on the fly and immediately gets tackled by the returner. even after the bounce, the returner was falling backwards and tried to catch it again but couldn't.

the ruling on the field. 15-yard penalty for fair catch interference. Whaaaaaaaa?

The ref cited a rule that when a fair catch is called the returned must have an uninterfered with attempt to catch it, even if it is muffed and still in the air.

But he attempted to catch it (twice) and failed. So they punish a Steeler for catching the ball.