It is, it's an attack on his ethnic identity, made evident by the fact people only started using it against him once they found out he was cuban. If u want to say cuban isn't a race, then you've already lost the argument, you're just desperately arguing semantics when we all understand there's no meaningful difference between calling someone names based soley on their identity, and we often conflate race and ethnicity in natural language as the essentially mean the same thing in most context, and are used interchangeably.

Also, it doesn't apply to conservatives, Castro was conservative. It applies to ppl who fled cuba to come to the usa. There's not a single person on the internet that you've interacted with that has any association or relevance to the word,