It's just a well timed photo on a cloudy day. There's a show on the stage in front of the castle every few hours and at the end they set of fireworks. What you are seeing is the second set of fireworks just going off.
It looks a little too light for the fire works show. Much less the second set. It seems a little pointless to have fireworks during the day as you wouldn't be able to see them well.
Trust me that's what it is, I live in Orlando and have seen it many, many times. Go to the end of this video and you'll see them go off: https://www.youtube.com/watch?v=VyRHkAQ2wSM
Call 9-1-1