Or, rather, he hasn't (yet) been found not-guilty of filing a false election return. That probably will happen later.
The news that the Court of Appeal has overturned the guilty verdict against John Banks' for knowingly filing a false election return in relation to his failed 2010 Auckland mayoral campaign is not surprising. To understand why, you need to remember the basis on which he was found guilty.
Essentially, it boiled down to what happened at a lunch held at Kim Dotcom's mansion. Dotcom (along with his wife and then-bodyguard) gave one account of that lunch. Banks (and his wife) gave another. The judge preferred Dotcom's account, according to which Banks explicitly requested that a $50,000 donation be split into two gifts of $25,000. Having done so, the judge ruled, Banks could not then claim he didn't "know" the source of that money ... and so even though he failed to read the donations return prepared by his campaign's treasurer, he nevertheless "knew" it must be false (because the treasurer (who didn't know about the ruse) couldn't have listed Dotcom as the donor, as the law required).
Therefore, Banks' conviction boiled down to credibility - the judge thought he (and his wife) were less trustworthy in their account of that lunch than Dotcom and his wife and bodyguard.
However, after Banks' conviction, his wife turned into a bit of a cyber-Private Eye and managed to track down two American businessmen who she always claimed were also at the fateful lunch. These businessmen then gave affadavits that substantially backed Banks' (and Banks' wife) account of the lunch. It was these affadavits that then formed the main ground for Banks' appeal.
And they provided pretty good reasons for overturning the verdict. They represented the recollections of two non-aligned individuals (i.e. folks without any obvious axes to grind) about the events critical to Banks' guilt or innocence. So, as the Court of Appeal found:
 Based on Wylie J’s reasons, we have no doubt that he would have considered the new evidence very important. As we have already explained, the Crown relied for proof of knowledge on what was said at the lunch. Had Messrs Schaeffer and Karnes been called, the Judge may have rejected the evidence of the three principal Crown witnesses about the discussion between Messrs Banks and Dotcom. We note too that some of the evidence on which the Judge relied to discount Mrs Banks’s evidence was neutral; for example, it was not in dispute that Mr Banks spoke to Mr Dotcom about donations at the mansion.
 At the risk of labouring the obvious, we are not suggesting that the evidence of the Crown witnesses was in fact unreliable or untruthful. The trial court will establish where the truth lies. Our decision establishes only that the new evidence is apparently reliable and, if accepted, plainly capable of changing the outcome.
Note this last bit. The Court of Appeal isn't saying that these witnesses conclusively prove Banks is innocent of the charges. It simply is saying that if you believe their accounts (which support Banks and his wife) over those of Dotcom and his "team", then Banks is innocent. Which again comes down to a question of credibility - which can only really be assessed by a judge hearing from the various parties at trial. Meaning that there'll have to be a retrial to allow this to occur.
Now, at the risk of being proven wrong yet again, allow me to venture a tentative prediction about the result of that retrial. The thing I've always found incomprehensible about the Banks saga is the question of motive. As I wrote here, for instance:
... one thing still amazes me about all of this. Banks' fall from grace stems from knowingly hiding a donation to a campaign that he lost, from a donor who (whilst he since has become somewhat more notorious) wasn't particularly important or noteworthy at the time. All I can think is that he cooked up a scheme to hide Dotcom's identity in case he won (without perhaps even being conscious that what he was doing was unlawful - did he think he was still playing by the rules he was used to from the more unregulated days he spent in Parliament?), and then forgot to change things when he lost. Which is not to forgive or excuse Mr Banks ... but it just seems such a silly, silly way to end your career in disgrace.
So if a judge in a future trial decides that these new witnesses make Banks' account of what happened at the Dotcom mansion more believable than Dotcom's story, I can accept that.