I don't think it's an Echo goof (since people besides us can understand the Vanu), it's just a cultural difference.
As you noted, the Sundrop Dance is based on Haka, a traditional war dance of the Maori people. Like the Sundrop Dance, its purpose is to psyche up the dancer(s) and intimidate their opponent(s). It's basically a challenge, "come get some!"
From our point of view, it's just a silly and goofy dance, since we're far more prone to immediately getting to the stabbing and shooting. It's very important to the Vanu, however, because it's a part of their history and culture, and allows them to resolve conflicts without bloodshed. (Unless you're dealing with the Vundu, but we all know they're jerkholes anyway. Maybe I should try using it the next time I'm sent on a mission to steal their food...?)