Many have dual citizenship, pretty common thing. What language they speak at home has no bearing on anything.
In Fedors case, who knows where his true allegiance will be in the future. He seems like a really great guy. The fact that he grew up in Russia will always be there for him as he probably still has family and friends and good memories from there and that will never go away, and he should not be faulted for.
Best to support him for who he has become, and not worry about where he came from as I'm sure he's got enough on his plate at the young age he is. He is doing a great job at becoming someone to be respected in my book.