It was a track day - enter at your own risk.
Was it his fault?
Rules of the day:
Overtaking by consent only - the overtakee signals consent using their indicators.
Overtaking on straights only - issue - the 'ring's a bit short on straights.
Hmmm, having watched the video several times now and knowing how trackdays/Nurburgring work, if people wait for the cars in front to indicate, it would be renamed the M25 on a busy day!
You can clearly see you move over to the right, Vergers thought it was clear, then as he commits, you moved back over to the left and he had nowhere to go. The speed you were travelling at, there was no need for you to take the "racing line" on that section.
I would have done exactly the same had I been driving, thinking you had moved over to let him through. Is it possible your mirrors had broken down?
Sorry, but although by rights you feel he was at fault, with the experience you have on track days and also the Nurburgring, I think you and I both I both know who was at fault.
Yours
Rosco (logged in on Daves account)