That was my immediate reaction, too. However, it doesn't necessarily have to be someone who was in the room. Apparently, the notes on the meeting went out, and that's when the scramble began to do damage control. The leak may have come from someone at that point.
The more sensitive details may have been prevented from leaking by this action, but the story of tRump's big mouth got out. Any number of people in the White House may be rightfully freaking out about the man in the oval office and the risk to the U.S. by him being there. The leaks aren't likely to stop, the firing of James Comey in an attempt to get someone in that position who will investigate and prosecute them notwithstanding. Fortunately.