Let me try this again.
Let's say we form a company to develop a web layout engine. We haven't made anything yet, and we're wondering if it would be better to make our layout engine closed source or open. We decide to go with open. Why? Because we're fed up with having to support slow, non-standards-compliant browsers for our web apps. If our fast, standards-compliant layout engine is open source, maybe more browsers will use it, and web development will be less sucky for us in the future.
It turns out that there's already some great open source code called KHTML that we can build on to create our engine, and it's licensed with the LGPL. Well, that's no problem, because we decided our layout engine was going to be open source anyway. So why not fork it? We don't have to, but it's good code, so we might as well. Thus, our open source layout engine ends up being based on KHTML. But it was not our decision to use KHTML that made our engine open source. We decided that it was going to be open source, irrespective of whether we decided to use KHTML.
Likewise, Apple chose whether or not WebKit would be open source, irrespective of whether they decided to use KHTML.
You seem to be making the argument that Apple just decided to base WebKit on KHTML without much concern for the licensing implications, and inadvertently ended up "stuck" with a WebKit that must adhere to the LGPL. Hence, Steve Jobs is disingenuously suggesting that WebKit was intentionally open source. And what I'm saying is, given Apple's long history of tight control over its software, not to mention their willingness to rewrite their software from scratch, that assumption just isn't credible. Whereas they have credible, self-interested motives for creating an open source layout engine, just like Google has credible self-interested motives for making Android open source.