Anxiety is not just a disorder, it is a natural reaction to life stress. It is only an issue when it becomes disproportionate or constantly/frequently present.
We are all going to feel anxious at some point - about a deadline, about a difficult personal situation, about health issues, about an issue which is outside of our control. It's too long since I did training on this to remember all the technical stuff, but essentially this is a response which is connected to the "fight or flight" survival instinct.
Removing a whole bunch of potential stressors from life - no exams, no PE, no having to see that friend who you fell out with last week, no difficult maths homework, no so-and-so teacher who shouts - is naturally going to make a mentally healthy person less anxious (whereas it might make a person who is mentally unwell more stressed, as these every day stressors might have acted as a distraction from their underlying problems). But it may also mean that, as well as being less anxious, they could be more depressed, more lethargic, lacking motivation, feeling lonely...