Thanksgiving is obviously just a US holiday. But AF knows that and prices accordingly, because a lot of US americans like to use that week to travel, and the US is one of the larger markets for AF/KLM. So they will have no problem filling their winter schedule flights, and a nice profitable price.

Kind of like reserving a flight to Asia during Spring Festival/Chinese New Year. Yeah, it's far out if you look 330 days in advance, but it's also the world's largest human migration in current times......and flights are priced accordingly.