Well besides the CAI and the Exhaust (including hfc and headers) he isn't getting an hp gain with any of that. Hes maybe pushing 360 hp with everything.
Plus its not all about having the best performance parts on the car, It's also about the driver who drives it. Now I understand the difference of a boosted car racing a non boosted car, also by type of boost ; SC, T, or TT.
If you have 2 people racing the same car and one can shift more efficiently than the other, well one car is going to be faster than the other.
Stickers, blades and spoiler don't make you faster.. (unless you stick the +5 hp sticker on them lol)
He could have taken that 9k and shoved an SC or T in there. If he was looking used maybe TT.
Then at that point yeah his car doesn't look like much on the outside but will whip a lot more and actually win.