Keith “haha”

Someone explain to me Keith’s use of “haha”. In the U.S., and possibly Canada, “haha” is meant to indicate something funny. But Keith’s use of it seems to be completely independent of humor. He’ll write stuff like, “Haha. My pet gerbil of 10 years died yesterday. It drowned in Drano. Twice.” So yeah, I have no idea what “haha” means.