You are presuming it's not true because the NHL couldn't corroborate. This is a very, very dangerous assumption. Truth is an absolute defense to defamation, and if the poster is sued, that leads to a period of discovery where Cole is compelled to provide mountains of evidence as well, and if any part of it holds up, then he loses and is basically proved guilty in the public consciousness.
I would take this to be exactly what it appears to be- a likely true story from somebody who wants to remain anonymous at all costs, even if that means Cole doesn't face further league punishment. A perfectly logical position given the absolutely disgusting displays we've seen from hockey fans over the last week.
The NHL couldn't get in contact with the accuser, and without that cooperation it'd be near impossible to corroborate anything. But that doesn't mean any of the allegations were proved false, either.
Could be true, could be false. We'll have to live with never actually knowing, but young women and girls will be more cautious around Ian Cole in the future, and that may ultimately have been the entire intent.