Correct it was an F4 not a Lightning. I was on VASS at the time. It was not launched at a bus or anything else it was an electrical fault that triggered the release, but as you say it luckily fell in the Eden estuary.

You are correct.
I think the bus as a "target" was speculation.
The guys in the Q shed were very fortunate, especially the one who was stood next to the aircraft.
I do not recall any answer as to why or where the spurious voltage that, allegedly, caused the launch came from.

Even the captive AIM-9s could be hazardous. One evening, we had a young lady weapons tech doing power-on ground checks on an A-7D with a captive AIM-9 installed. The seeker head sat nearly abeam and just below the cockpit. When she selected the station, the seeker didn't cage but oscillated wildly, shattering the dome and throwing various pieces of shrapnel all around and near the cockpit. :eek:

(BTW, a very fine looking young lady from a male perspective and fortunately not a scratch on her or hair out of place after the incident, just a good story to tell. :})