Nine times out of ten, when you structure your code/models well, optimization will become obvious. How many times have you seen a hornets nest and found it totally suboptimal, where upon restructuring it, lots of redundancies became extremely obvious.
A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away.
- Antoine de Saint-Exupery
A well structured system will be minimal in nature, and due to it's minimal nature it will be optimized because how little there is to it relates directly to how little it does to accomplish it's goal.
To expound upon the point other's have taken away from this, it's also completely accurate to see the statement as identifying the relation between code and data. That relation is thusly: If you change the structure of your data, you will need to change your code to respect the altered structure. If you wish to optimize your code, chances are you will need to change the structure of your data to make your code capable of handling the data more optimally.
That said, there is a totally separate possibility that was being eluded to here, and that would be that this fellow having relations with YCombinator may be referring to code AS data in the LISP tradition of homoiconicity. It's a stretch to surmise this as the meaning in my mind, but it is YCombinator so I wouldn't rule out that the quote is simply saying LISPers are the "Best Programmer"s.