There are many rules for Buddhist monks. The Buddha said some are major rules you have to follow and some are minor rules you can choose to disregard. But which was which was never clarified.
So it's a matter of interpretation. For instance one rule is that a monk can't eat after midday. Is that a major or a minor rule? Nobody knows for sure, but generally Tibetan monks are more flexible about these kinds of things, following the idea that though ideally you'd like to follow all the rules, in modern society out of compassion to others it is best to not insist on the minor rules, where it is up to your interpretation what you consider minor rules.
One of the rules is that a male monk shouldn't travel alone with a woman because that can lead to suspicion amongst others who might think that they are lovers, impacting on the woman.
where again lay people might think they are flirting. So preferably another man would be present when a male monk is talking to a woman.
Those are the Therevadhan monk's robes. As a Tibetan he'd be following a slightly different set of rules but similar.
But in modern society a monk might well judge that there is no risk of any of that causing confusion or offence. After all it is normal in modern society for a woman to sit next to a man while traveling with no implications at all :). Then it would be a matter whether he is okay with disregarding this and treating it as a minor rule.
Or maybe it was something else altogether? There are lots of rules, also it might not be to do with his vows but for some other reason we don't know about.