Passed smog...but what does it mean??

Just passed my bi-annual smog test on Saturday. I actually passed most of the measurements by a wide margin...except one.

At 15 mph, the maximum allowable emissions of HC (hydrocarbons?) is 54 PPM. And I came in at 53 PPM.

So I was wondering what that actually means. And what can be done to lower that number? Is there one specific component that is responsible?

I have a bored-out TB, K&N FIPK, Borla header, Carsound cat, and Gibson cat-back.

This is just a guess, but all the mods you have listed are to pump more air through the motor, tb, filter exc. the more air you cram through the motor the more fuel is needed to prevent the motor from leaning out. your computer compensates for the added air by adding more fuel. all the extra fuel, and air might be causing those numbers. just my $.02.