DDR3 traces need to be length matched, because at 800MHz (the slowest "standard" rate, though I think you can drop to 666MHz safely) the value on the pins is changing every 1.25ns, and having traces of different lengths means you probably won't see the right values on all the pins at the same moment. Length matching produces the squiggles.

The diagonal orientation of the DDR3 chip and corresponding diagonal traces I suspect is a choice made by the author to ease the layout process - it's more likely that is hand laid out to get traces of somewhat similar length with a minimum of fuss, followed by a length matching tool. A non-standard orientation can cause issues with pick-and-place machinery, which usually will handle 90 degrees fine, and _often_ 45 degrees fine, but (AFAIK) _rarely_ anything else, but that's not a problem for the author because he's assembling it himself. A diagonal IC also usually results in wasted space, which you can see in the empty areas of the resulting board. A 90 degree orientation may have allowed for a few more decoupling capacitor banks, but since his board works, who am I to sit here and judge?