I don't think it's fair to judge the ethics of a person by how nicely they respond to being screwed over.
But, since we don't really know all the facts, if this was a mutual parting of ways, then I agree that it's a terrible thing to do.
The bottom line is we really don't know what happened. I can at least see how a reasonable person could walk this path if they feel they've been maligned.
It's that "rightfully yours" bit that really bothers me. Where does that come from and why is it so obviously rightfully yours? It takes some gumption to assume you're in the right. This land is rightfully mine because I bought it from someone else who genocided a people, but okay great, it's rightfully mine, I feel super great about it.
The one's filing them and demanding what's rightfully theirs are selfish, the one's not filing patents are less selfish.