You might look on Wikipedia:
a blog ...
is a discussion or informational site published on the World Wide Web and consisting of discrete entries ("posts") typically displayed in reverse chronological order (the most recent post appears first).
is a technology used to store complex structured and unstructured information used by a computer system. The initial use of the term was in connection with expert systems
So I think the distinction is that a blog is a set of posts written by and for human beings, while a KB is structured, and supposed to somehow be processable and processed by software. Read also about inference engines (e.g. CLIPS ...)