There can be a marked increase in the incidence of something, but still be a low risk.
For example, in the study from the armed forces on myocarditis they found the risk to be low (23 cases from 2.8 million doses), but elevated relative to expectations for military receiving a second dose (19 from 0.5 million vs expectation of 0 to 10).
From the study: "The observed number of male military members who experienced myocarditis after their second dose of mRNA vaccine, while relatively small, is substantially higher than the expected number."