The source article is here. The numbers are not how much of the total the subgroups make up, they are how quickly each subgroup is growing. The text continues:
The number critically ill with covid-19 in that age group grew by about 30% in the week before January 2nd, and also in the following week—but by just 7% in the week after that (see chart 2). By contrast, among those aged between 40 and 55 (who were vaccinated at a much lower rate at the time) the weekly change in the number of critically ill remained constant, with a 20-30% increase in each of those three weeks.
The source article is here. The numbers are not how much of the total the subgroups make up, they are how quickly each subgroup is growing. The text continues: