"The king's roads have nothing to do with the master of Lost Hope." And try he may, Strange can't entirely hide the tone of 'duh, Foster' in his voice. He doesn't see why this is so frustrating, despite the fact that Strange's explanation wasn't entirely the best. There's a pause as Strange goes over what he said before Strange realizes he's made an essential mistake in his explanations.

"The king's roads were built by John Uskglass. They are literal roads and help connect Britain to faerie lands. They were hidden behind the mirrors of my world but not anymore. And, as they were built by Uskglass, I don't expect to find them in this section of faerie. Uskglass also goes by the Raven King, who I mentioned earlier."

The fact that John Uskglass is the Raven King (and also has a whole bunch of other names) is something that Strange takes as information that every person knows except that no you idiot, there's only one other person in the carnival who gives a damn about the Raven King in the first place. Still, he can't help but wonder, could it really be this simple an answer to the problems Foster has understanding his explanations? (It won't be. But Strange lives in hope a little bit.)