If I invite somebody into my garden I am perfectly entitled to insist that they wear a facemask before they enter, whether or not it is the law to do so. Similarly if I am a nervous car passenger and I don't like being driven fast, I have every right to make it clear to a taxi driver that I will only become his fare if he limits his speed to 45mph. Just because the national speed limit is 60/70mph doesn't mean that I'm not allowed to impose such a stipulation. Similarly TOCs have a right to stipulate that passengers must wear facemasks even if it isn't the law to wear one in a particular country. You could say that it's part of their duty of care to passengers to insist that they must be worn.