See figure 2. Double shot of Moderna has higher chance of myocarditis than covid does. They do add this to the conclusions of the paper, but they defocus it by talking about the populations as one large unbroken dataset.

When looking at people under 40, the risks for myocarditis are higher amongst Moderna double shot patients than for covid infections.

Averages are misleading. All the risk is concentrated in the group under 40, where it is higher for the vaccine.