In this case the operator's usage of the word troll to describe what happened is telling. Anyone can send any kind of threatening letter they want, and they are free to report you for non-compliance, but that doesn't mean any action will be taken against you, let alone actual fines.

IANAL, but IMHO the chances of any solo forum operator being sanctioned by EU regulators is effectively nil—the purpose of the law is specifically to address usage of personal data, not old-school off-the-shelf forums and other one-off websites where the scope of the data is essentially the core of the service itself.

You can argue the only thing that matters is the end result, but I'm not sure there's any way to write meaningful privacy regulation that will not generate a huge wave of FUD, especially with the traditional SV stance that we ought by default to have carte blanche to monetize user data in any way that's effective.