No, it's not ironic at all. It's not asking people to stop using .io. It's asking people using .io to support a fund that supposedly helps the cause of natives of the island.
By using .io TLD, they are submitting to the UK government on what should be theirs. It may be like rebels claiming a territorial independence but then still pay taxes to the government for that particular territory.
Most non-violent independentists in western countries pay taxes. Actually, even most violent independentists pay taxes as well so they can conduct their activities without attracting attention from the government.
Did you read the link?