1. Sartorialist David Tang suggests calling the WH social secretary for advice:

https://next.ft.com/content/1b617614-0a73-11e3-9cec-00144feabdc0

"If, however, you are going to a small gathering or a fairly intimate repast (of no more than a dozen, say), then it would be perfectly in order to telephone the presidential social secretary at the White House for the exact dress code: not to ascertain what you are not required to wear, but what you are asked to wear."

2. from the pix i've seen all the other folks who attended the meeting wore suits. J. Cole stuck out. i suspect that happened b/c those other ppl were (properly) advised to wear suits. maybe b/c they or their ppl called the WH social secretary. or b/c they just have common sense.