A little misunderstanding all round, I feel. As this study involves voice sampling, I suspect that intonation, pronunciation, accent and so on, all play their part in this. Hence 'non-native' may be intended in this case to mean 'non-American'.
As a UK citizen who happens to have been born in Scotland, I have become used to a liberal interpretation of 'England' by those less familiar with the structure of the UK.
Besides, I spend a chunk of my time right by Moffett field, give the guy a break!