Are you talking about the Legend of Korra? (I love that show btw).

Bisexual is not straight, or homosexual. Bisexual means that someone doesn't judge sexual/romantic partners based by their gender; they can be attracted to both males or females.

Personally, I LOVED that ending. It's clear but could be missed by children, which I think is a nice line as a large chunk of society is still ridiculously homophobic in regards to including non-straight couples in the media, particularly in children's media.

And it made sense for Korra and Asami, because Asami is the only person that Korra continued to confide in throughout everything. You could see them becoming closer throughout the final season; I was actually not overly surprised and was rooting for them!

If you are somehow talking about a different show... well, my opinion still stands. I think it's great to show that people aren't always defined by just one set of criteria. I also think that having it come unannounced is also great, because it helps to expose people's bias' (such as it did for you!) and point out that you can't always just make assumptions about people.