He saw a dragon flying over Kings Landing which might not have been this dragon. Still, even if it was it's obvious it was just something momentary rather than omniscient knowledge.
It was the exact same shot. It's clear the writers want us to twig that Bran saw this happen in his 'visions'. Why shouldn't he be able to see more glimpses of the future if he has the power to go to any moment in the past? Why is it obvious that he can only see that one moment? I must be missing something here.