If the frame is from a Victoria your seller could technically be right in calling it a Victoria, regardless of what engine or tank or forks are fitted.
Many State authorities regard the frame or chassis as being the major identifying part of a vehicle regardless of what else has been done to it. Its like a hot rodder saying he drives a '27 T Ford bucket when all that remains of the original '27 T Ford is the chassis rails. The engine, drive train, wheels,etc,etc are all from something else. It's still seen as a '27 T Ford.
Maybe this bike fits in the same category.
Cheers,