The way you describle Boards of Canada seems accurate, and a good way to explain how they are not trip-hop. I've never heard the term illbient applied to them though. Not saying it's not accurate, I don't really know what illbient is to tell you the truth. From my experience people usually refer to Boards of Canada as IDM...which is broad in itself. They're definitely part ambient, but overall I think their vibe is too lively and interesting to be considered strictly ambient. And I suppose that's where 'illbient' comes in. Kind of like how when I first heard stuff like Prefuse 73 (IDM combined with hip-hop) I called it trip-hop. It wasn't just IDM, and it was too IDM to just be called hip-hop. So I can see it...illbient. Ambient that's cool, fun, dope etc.
