It started as a Konqueror fork mostly because Jobs wanted a browser on OS X and Ken was initially tasked with it (back then the mac had IE for mac). One person writing a browser from scratch even back then seemed an impossible challenge so he took a look to see if he could use most of Konqueror as an initial starting base.

[0]: The book has some interesting stories, but I find it hard to recommend because it's weirdly written for an extremely non-technical audience (using grandma like analogies to explain basic concepts, the analogies are so basic they do more to obscure than explain - e.g. the filesystem is like a 'cabinet for files'). It doesn't often get into the weeds of the interesting technical details - which is disappointing since 90% of readers are probably technical. The stories in it are still good though and Ken has a lot of insight into the iPhone development story since he was there.