There are no sanctions on refuelling Russian owned planes, or boats, outside of Russia. There are sanctions on exporting jet fuel, and its additives, to Russia, and on the use of US, and multiple other countries, made components to service them anywhere, but filling the tanks using local jet fuel on foreign soil is not covered.
Interestingly, at least one country in the region does actively aid Russia in evading sanctions, but it's not Thailand, so no use to the bashers.
"“Of course sanctions affect flight safety,” said Russian aviation analyst Andrei Menshenin in an interview. “They can’t not affect it.” But he said Russian airlines had softened the impact by importing spare parts and even fully reconditioned engines through Central Asia, Turkey, Singapore, Iran and other countries."
Russian air passengers face peril as planes show strain of sanctions - The Washington Post