Anxiety also causes you to perceive normal bodily sensations, that you otherwise filtered out, with heightened sensitivity.
"With health anxiety there is the misinterpretation of discomfort and normal bodily sensations as dangerous. The body is very noisy. Healthy human bodies produce all sorts of physical symptoms that might be uncomfortable, unexpected, and unwanted, but not dangerous." https://adaa.org/learn-from-us/from-the-experts/blog-posts/c...
Add the context, and the potential for disinformation goes away: "Vaccines cause myocarditis, but overall at a lower rate than the disease itself. Additionally, the disease has many other, much more significant, risks that are mitigated by vaccination."
The point I'm making is that disinformation is a psychological effect. A statement can be factually true and still be disinformation ("100% of child abusers found to have consumed dihydrogen monoxide", etc.)
What you say could be true if this person had experienced such events prior to vaccination as well.
Otherwise the probability of having a first episode of ectopic beats within 28 days of the vaccine is far less likely to be due to anxiety in the absense of previous history of anxiety, let alone one with rare symptomatology.