I don’t think it is a payment issue. At least in Brazil (where I live), a registration (which can be done directly with the .br registrar, not necessarily third parties) costs less than 10 USD a year.
vlemmy.net was registered less than 2 months ago, for 5 years. I suppose (hope) it was already paid for 5 years.
it’s strange that it’s parked at a dynamic dns service though
Yes and yes.
You can have multiple communities with the same name in different instances, and not necessarily about the same subject.
You can also have not only the same display name as multiple other users, but even the same username, if not in the same instance.