Quick summary of methodology here.

The analysis is based on PCR positivity rates (PR). Basically they compare the % positive for those tested >=146 days after 2nd jab, vs the % positive for those tested <146 days.

Specifically for the >60's, they had 182 positive tests out of 7021 tests in the group >=146 days after vaccination, and 19 out of 2164 test positive in the group <146 days after infection.

182/7021 = 2.6% PR 19/216 = 0.9% PR

Now I cannot for the life of me understand how this is relevant to the conclusion reached. In my mind this is more reflective of whether or not someone gets tested, which is highly tied to the symptoms displayed. e.g. It's been made public knowledge that Delta is associated with things like headaches and sneezing, so perhaps more people are testing now when they have a cold - that brings down the PR. There's probably a number of other possible explanations too.

In short - I'd take it with a pinch of salt.