Your definition is an island. There are many tipes of irony. You've just limited yourself to the dramatic irony. Stricto sensu, in spanish irony is the rhethorical figure. Everything else is an elaboration over that.
Many people ask, or are unsure of what irony is.
Socratic (dramatic) irony, the original word as defined by Socrates (obviously), refers to any situation in a work of dramatic literature when the interest in the work is drawn through the audience being aware of a key fact that the dramatic (and in this case ironic) subject is not.
I just think that, as someone who seems to be an island in an ocean of people who misuse or misunderstand the word, this is one of my favorite strips ever.