In Tsukihime, he just says vague words about revenge, leaving the players to piece together by themselves that Roa is the one who sullied his liege, whatever that means. Then in this week's interview, Nasu said Melty would give further hints but still not reveal the answer to Vlov's mysteries. And yet, here Vlov is openly stating that the target of his revenge is Roa. That means this wasn't the big twist and there's actually more to Vlov's character to see later. That's honestly a relief. His character is sorta lacking in meat and I was worried that the Roa reveal was going to be all we still get.
Well, we one thing we still don't know is what exactly Roa did to Zaria. That's one thing with potential for his backstory.