Not even close.  First of all to prove liable/slander (at least in the US) the person making the statement has to KNOWINGLY make a false statement.  The mere fact that the statement is false is not sufficient.  So if someone posted some faked screenshots/records/scanned docs showing Pirate selling the deposited coins and transferring money to a bank account in the cayman islands AND it turned out to be false AND you could prove the person posting it knew it was false (faked it himself) AND that statement caused a loss AND you could prove the loss was directly related to the false statement (coincidence is not correlation under the law either) AND you suffered a loss you would have a case.

Even then it would be very hard to prove and win and the damages likely would be far beyond anything the defendant could be paid so almost certainly the judge would reduce them.

Another way to look at it is IF you run a business that is 100% legit but it utterly indistinguishable from a ponzi scheme then guess what .... the risk that it will be confused with a ponzi scheme and you may suffer a lack of liquidity as a result is a business risk.  A risk that both the operator of the business and the investors should have considered.   Lets assume Pirate operation was 100% legit.  Could he have done anything to mitigate that risk?  Transparency?  Delayed withdrawals?  Working with a smaller pool of high net worth investors?  Since he chose NOT to take steps to mitigate that risk factor and the "investors" decided to ignore that risk factor any losses are solely the fault of the operator and investors.