Obviously that's not true if the genetic infomation Oxford University obtained showed a distinct difference in DNA to that of the wider English population.
If as you say most arent Cornish then the DNA study would have showed that. It seemed to show the opposite.
DNA says they are a distinct people than those from Devon and most of the rest of England.
So yes,they are from a different genetic background. There's no debating that. Oxford University mapped the whole of Britian.