I mean the only way people could be "genetically American" would be if they were native Americans (to some degree). Not just the descendants of europeans settlers.

I cannot tell if you're being serious. I do not think you are. But just in case, I'll pretend you're being genuine.

An American can be many different things from all over the world. They can be South American, North American, Canadian, etc. And they can have origins from other countries.

Being Irish and having a genetic similarity to an American quite obviously means the American is Irish or part Irish, in the context of this conversation and especially my statement.

This is why labels such as "Irish American" exist.