Hey folks,
Thanks for the further responses. Like I said in my initial post it was pretty spectacular stuff, in that you are spot on. The primary reason it stood out was because every other flight for several hours worth of spotting followed a pretty obvious pattern, even to a novice. Some kind of training/practice route I suspect.
This particular flight just lit the blue touch paper and, as you say, was gone in seconds. Just glad I caught him at it tbh :-)