Yes, it’s a little slighting. Am I guilty of countless acts of the same? Um, yes. This may change as the definition of self-publishing evolves, but we’re not all the way there yet. So unless you’ve sold a zillion copies of your self-published book, best not to bring it up too soon.
I’m a self-published author who just completed his second novel. An agent once told me I shouldn’t state that I’m a self-published author in my query letter because it shows that no one has taken an interest in my writing and therefore I had to publish my own books. Apart from being rather insulting, does this agent have a point?