Another factor is that the student is protecting their parents from doing something that they will likely later regret.

I've known a number of folks who came out to their parents and got fearful and hostile responses — which the parents later apologized for and tried to make amends for. This seems to be a pretty common pattern, in fact. Broadly, people want to have good relations with their families, but they may not always act that way in the moment — and they come to regret actions that harm those relations.

Putting people in situations where they will predictably behave in ways they will later regret is widely regarded to be pretty crappy social behavior. It's certainly not the sort of thing that people endorse doing to those they love. If avoiding that situation requires a certain amount of narrowly targeted deception, so be it.

Adopting a deontological-style rule of not explicitly lying (using evasion or refusing to answer, for instance) may be worthwhile. Avoiding deception in general is a good idea for consensual relationships willingly entered and willingly left. Parent/child is not that kind of relationship, though — not in our society and economy. Even though it would be desirable to cultivate a world in which there were no violent outbursts in response to true facts, it would be negligence to the point of malice to advise people in dependent social situations to pretend that they live in such a world.