Don't you see the difference? US pressured France and Spain to deny their airspace, but landing in Vienna was pilot's call. The pilot could have returned to Russia if they wanted. They erred on the caution side, and they were greeted by Austria's president. So shady, but not illegal, compared to for example the poisoning of Russia's dissidents by FSB.
What do you think would happen if Ryanair's pilot refuse to cooperate with Belarus's request?