@DY. I will assume the “they” in your question refers to those who asked the question of R’ Moshe. “They” wanted to give vacation from yeshiva during this week (I dont remember if it was instead of some other week, or not) because the parents were already off from work. In his answer he replies they should not, and as an aside, he says taking vacations during this time (which I understand to mean, a trip to disney or wherever is not appropriate either) even though the parents are off from work is “mechuar” (which I will translate as not appropriate).
The OP seems to be using the word vacation as in taking a vacation day from work, by the juxtaposition to his Sunday comment. then again, trying to make sense of a trollish comment is useless.
Both the I’M and the N’G are not discussing taking off from work as is implied by the OP.