It's one result. Don't really think one game should change how a managers abilities are percieved. Because, as another poster made reference to, despite this win, they've lost at home to Wolves, West Brom, Bolton and others.
What this result will do though, is buy him some time. If they beat Stoke and Fulham and start to take a few points from their away games then yes, this could be seen as a turning point and opinions of him may slowly but surely start to change. But to change your view of him just off this is going a bit too far.
We saw last year with Wolves, they beat City, United, Chelsea and Liverpool. That's four great results against the big boys. But they only stayed up by a point. For all we know, this could well be a one off for Blackburn. Kean still has a lot of work to do in order to prove himself.