When someone becomes a public figure, there is always the risk that others will use them as a figurehead for something which they themselves would not support. Sad, but true.
I don't see Captain Sir Tom's story as anything to do with nationalism, white or otherwise. I see it as a story of human desire to do something to help in times of great need. He couldn't do much, but what he could do, he did, and it took off.
But I'm white, so maybe I don't see or experience things that black people do. When a black person says something is racist, perhaps we should ask why they think that, rather than shoot them.