The "flashing lights" were the sequenced flashing lights on the approach lighting system reflecting off low cloud and mist, the "aliens" spotted by the locals were the Woodbridge RFFS team in their gear and at least one sketch made by a local of the "spacecraft" looked just like a D21 drone.
The Americans won't discuss Special Ops with anyone and I'm sure helium balloons wouldn't be flown around an active airfield without someone being notified.