User blog comment:Ajrep1994/Yang and Ruby are half sisters/@comment-3146930-20140723223108/@comment-72.49.131.154-20140723233403

Ok, I'm confused. This blog post by Monty says they're half-sisters, but one of his previous posts in the same blog (Reference #7 in Ruby's wiki entry) has him saying they're definately not STEP-sisters. Aren't those two statements mutually exclusive, or am I misunderstanding the definition of a step-sister?