KDE is not a company and WebKit originated as a fork from KHTML, KDE's HTML rendering engine used in Konqueror. Too much credit is often ascribed to Apple for appropriating the engine on to a popular piece of software (OS X).

They did applied polish to it though and also built a new Javascript engine. I don't know who contributed what, but today's WebKit is a lot better than what KHTML was before being forked. I was once a KDE user and the first thing I did after a fresh install was to replace Konqueror.

But yes, truth be told, the KDE developers that worked on KHTML deserve a lot of credit.