A non-factual statement is not necessarily a lie.
At this point, we've only got the prosecutor's side of this. If it is a discrepancy between Libby's memory and that of media people (like Judith Miller), then I can see a number of ways that we can have different recollections.
Faulty memory, speculative statements, different opinions, etc.
Innocent until proven guilty. We haven't heard his side yet. (In fact, there aren't too many who have a grasp of what the crime is.)
That depends on what the definition of "is" is.