yep, I always find surveys to be a very lazy way of "doing science" but that is probably for another thread. The results of this survey do create an interesting (and in my opinion, believable) talking point, and maybe can lead to a better researched paper on the subject.
I personally think that PhD students are more likely going to be cautious of anything they don't have a good understanding of. They would (imo) be inclined to do better research into the pros/cons of vaccination, which is not easy to do right now with all the noise online.