Not quite how that works. Romano Britons we’re still Roman citizens and would have identified as such. Plus he came from rich influential parents. He would have spoken old Latin.
The English didn’t become English until later and after the Romans had abandoned Britannia. This would have been prior to the Saxon invasion. I doubt he or anyone else at that time called themselves English or considered himself one. Certainly not in 386 AD.
en.m.wikipedia.org
But yes you can claim he comes from the place they hate. But he wouldn’t be English, just from the same place the English claim to be from. And I doubt most people would know that anyways.
Happy St Patty’s Day! You’re Irish today whether you like it or not