Because he has no idea what he's doing. He just saw the items the player used and thought "Hey, I should put a guide on mobafire!" The dude most likely started fort pot with pots, and used 6% life steal for quints, but now with the changes I would just start long sword 2 pots if I think I'm going to get pushed back by a stronger adc, or dorans if I want to fight. For masteries, I would go 19/0/11, you just try to get the 5 armor pen, and then go for the 3% leech in the utility tree. For items, the order seems right, but I'd go for a defensive item like banshees veil or warmogs instead of going for bork last. I'd only play this build if my comp looked like it might have a pokey aspect to it, otherwise you're better going regular adc build on ez.

just 1 question... why would you put points in lethality and frenzy if you have a crit chance of 0%?