A1 Studio doesn't really like to reference other characters it "owns" or it owns. The "owns" is in quotations cause, you know, anime studios can collaborate with some other company to get advertisement and more money for their product, but that doesn't mean the anime studio rightfully owns the whole franchise-thing. But! Anime companies can throw their own OCs into other peoples work and can make some really dumb cameos, like in Inou Battle Nichijou-kei no naka De, Trigger threw in Mako (from Kill la Kill) in one of the episodes. Why? CAUSE THEY'RE STUDIO TRIGGER. THEY DO WHAT THEY HEKKIN' WANT.
I don't know if this has nothing to do with this quote,
I can agree that studios sometimes have the right to put their characters in another just like trigger did, I'm not sure about the A1 one, but I don't think I ever saw another character from another anime in so far for me, I think it is just as you said.
however, let me remind you that cygames (the game company behind gbf, RoB, DL, and shadowverse) has once collaborated with atlus, the p5 collab in gbf, and reminder any company relation or premession made them put these p5 characters in.
they could've been just a gimmick characters of them, or maybe they just want to make us beileve that "yeah, let's put p5 characters as a reference" or maybe "we should refrence p5 characters to hint our upcoming collab for shadowverse" or something, however that's just a speculation, and I won't feel any hyped about it(or I could be)
In the end I really can't think if that's real for what I said, and let's see what will happen, I might be even wrong.
(edited by Yukapuyo)