As the National Review pointed out, the Defence Language Institute advised that many countries adopted the Western hand movement after the Gulf conflict:
This gesture, expressing connotations of 'I am winning,' historically is offensive to many Arabs. After the Gulf conflict, however, Middle Easterners of the Arabian Peninsula adopted this handmovement, along with the OK sign, as a symbol of cooperation toward freedom.
So, it doesn't seem to apply in Saudi Arabia and Trump is fine to thumbs up all he likes - at least by this example:
If the thumbs up is rude in Saudi then King Abdullah's been giving some cheeky gestures on his foreign visits https://t.co/LXHMuO4Cpp