Eye witness on rig
Having read the Mike McKay eye witness email it appears to fit with the scant info we know. He would not at the time be able to see the a/c (night) or have known its flight path. Seeing a cruise altitude flame trail would I think be possible given dark, clear skies and if he had his night vision.
A 10-15 second time frame makes it sound like a single catastrophic failure took the a/c down which would agree with the total lack of comms. This is probably the best (only?) available evidence so hopefully they will trawl/sonar the reported area.
Given that his identity has been released it is unlikely to be a hoax.