Splitting hairs, but

It's right there in their "definition". They are an association in the way the operate like no other trade union because they are hemmed in by RLA and are essentially many "local" unions negotiating on their own CBA's all under the umbrella of the Associations purview, guidance, and assistance.

So even according to them, they are small u union, but actually an capital A Association.

In the end, don't care what they are or aren't, the RLA is there to deal with, and hopefully our dues are being spent to our benefit as much as possible.