First of all, I'm always skeptical when its anonymous sources stating what when on. Given the hostility of the media against this president, I don't rule out made up stories. As for the basis of this story, the fact the meeting went on and discussed terrorism was public record. So just the fact that the meeting occurred does not verify the claim of WaPo. Finally, Trump as president does have latitude to share data with whomever he wants. If we have classified info that says Moscow airport is going to be bombed, I'd hope we share it even if its 'classified'. Maybe not share the details of how we got it, but I'd hope we'd share the plot beforehand and not just wait for the event to show up on CNN.
My personal expectation is that he did share something classified, but in an appropriate manner expected of good partners in the fight against terror. I expect that WaPo took that knowledge and spun the story like he just gave up every state secret and missile launch code. And David and Sys, like well-trained lab rats, found the cheese from WaPo and immediate came running to show it.
In the end, its irrelevant. Whether he did or didn't share some 'classified' info doesn't impact me on iota. It doesn't impact the markets, the job economy, or anything that connects back to me, short or long-term. Its just fluff to keep those who already don't like him riled up. I imagine we'll keep seeing these types of stories every couple weeks until the mid-terms so that the anti-Trump platform (all the Dems have) is viable.