The study is on college kids.
If the dining hall at my college suddenly went vegetarian, I would have pretty much had to go along with it; it's the most convenient option, and often the only real choice to get something to eat between classes - going off campus would take too long. And then there is the case that your meal plan is only valid there, and in the case at the school I went to, you could not opt out of paying for the meal plan even if you wanted to, so you'd be flushing $500-$1000 down the drain.
> variables that influenced dining choices included the relative prices of vegetarian and non-vegetarian options
But if that's a very important factor and vegetarian was cheapest, anyone strapped for cash would always have chosen the vegetarian option even before this experiment, so nothing would change.
Also, from the actual abstract (https://www.pnas.org/content/early/2019/09/24/1907207116): "Linking sales data to participants’ previous meal purchases revealed that the largest effects were found in the quartile of diners with the lowest prior levels of vegetarian meal selection."
My understanding was that they went from three meat options to two, and I saw no indication in the abstract that they changed pricing (but I haven't read the paper), but yes, there are possible scenarios in which they were "forced" to eat non-meat.
More plausible, to me, is that most people who regularly eat meat are not that uptight about it, and willing to try other stuff without feeling victimized. But yes, I also know people who are the opposite.