I don't think the study shows that either. Generally the bulk of the cases and especially hospitalizations and deaths have been amongst unvaccinated. When you have 40% of a country unvaccinated and when those 40% tend to form social groups and closer connections you can't really look at the country as a whole.
At any rate, the methodology of the paper is just way off. If you truly wanted to understand the correlation between vaccination and infection rates you need to try to control for other factors. That is just experiment design 101. If you control for nothing while there are other significant factors then you get nothing. If the paper is saying "there can be high covid rates with 60%-70% vaccine coverage and the delta variants" then sure, but also duh.
At any rate, the methodology of the paper is just way off. If you truly wanted to understand the correlation between vaccination and infection rates you need to try to control for other factors. That is just experiment design 101. If you control for nothing while there are other significant factors then you get nothing. If the paper is saying "there can be high covid rates with 60%-70% vaccine coverage and the delta variants" then sure, but also duh.