I don't think the author of this article has interpreted this study correctly. She appears to be comparing the myocarditis rates in Supplementary Table 21 vs Ta

I don't think the author of this article has interpreted this study correctly. She appears to be comparing the myocarditis rates in Supplementary Table 21 vs Table 22 to get the numbers of 370 per million vs 500 per million, but those two tables represent two fundamentally different cohorts and cannot be compared straight across like that. Table 21 removes individuals from the cohort once they become vaccinated, whereas Table 22 continues to follow up with those individuals until the 12 month mark. It is entirely possible that many of the individuals that were removed from Table 21's cohort did go on to develop myocarditis, but they aren't included in the measured rate by virtue of being censored from the analysis. In other words, you would naturally expect the numbers in Table 21 to be lower than the numbers in Table 22 simply based on the fact that they are measuring two different things, and this has nothing to do with the actual risk of vaccination because this study wasn't trying to measure that in the first place. Given the above, the napkin math performed by the author pretty much comes across as nonsense. You can't play with the numbers like that because they don't actually mean what you think they mean.