Poor Jay, he's obviously suffering from have to conduct damage control day after day.
I can explain it to you but I can't understand it for you.
"Any man who thinks he can be happy and prosperous by letting the Government take care of him; better take a closer look at the American Indian." - Henry Ford
Corruptissima re publica plurimae leges; When the Republic is at its most corrupt the laws are most numerous. - Publius Cornelius Tacitus
It's not as cut and dry as it sounds. I'm not saying he didn't know. It would be more correct to say he wouldn't answer the question.
Perhaps it's because Jerusalem is not universally recognized as the capital by the international community and he didn't want to pulled into that debate.
That was a no win question.....he made the right choice by not stating one or the other, or even trying to explain, setting US foreign policy on such a contentious subject is not his job.