There are two possibilities. One and most likely it was an overspeed stop. The speed zone through EPCOT is 20MPH and drops to 15MPH approaching the station if the driver wasn't paying attention when the speed change occurred then would be going to fast when approaching the station and thats about where the train would come to a stop before allowing the driver to resume. Two it could have been a door alert, someone pushed on a door just enough to stop the train. Given that this was immediately after the speed zone change I would guess it was the overspeed stop. It is also possible the driver did this for some other reason intentionally (someone jumping over a railing, something on the track etc.)