Board Thread:General Discussion/@comment-70.64.83.111-20151103022126/@comment-4010415-20151115234428

That's pretty much it. Ruby grew up with Yang calling him uncle, so she started calling him uncle too, and since Yang grew up thinking Summer was her mother, none of the adults corrected this because they knew doing so would raise questions. Even if Ruby knows the truth now, that's not gonna stop her from calling him uncle. She loves him like family.

Though... we actually don't know if she knows the truth.