yes, it's evidence, naomi. If you give evidence in court, and it's untrue, it's still evidence. Evidence isn't the same as proof, it's just an element that can be presented, investigated, debated and accepted or rejected. In this case it looks as if it was insufficient to base a case on - but even that doesn't mean it was necessarily untrue.
Why it took the police so long to sort it out, I don't know. Perhaps it was because the allegations did look reliable and needed thorough investigation; but there may be other reasons.