There is a term for this: "irony of fate" [1].

Which is presumably where the confusion with irony (as a stand-alone word) comes from.

Interestingly enough, the term exists in a literal translation in other languages, too: "Ironie des Schicksals" in German, "ironie du sort" in French, and "ironia della sorte" in Italian.

[1] http://www.bartleby.com/81/8963.html