[BAReF00t]

TL;DR: He didn't!

He wrote a UI for a browser engine (Webkit, of couuurse). Using a UI toolkit (Qt). In a scripting language.

Which is more putting wallpaper on the walls than constructing the building or even painting the walls.

[BubRoss]

I don't know who would downvote this. There are lots of articles about someone creating their own browser and they all turn out to be a variation of 'they didn't create their own browser, they made their own skin'.

[detaro]

Many different browsers use the same engine at the core. That doesn't mean they aren't different pieces of software. just that they use the same engine.

(In this case, one might nitpick that "programmed" suggests something different, but I don't think that's clear cut)