My criticisms would be:

1. The sample size is small, and the authors dont give any sort of demographic data about the subjects used in the experiments, so we cant say for certain that there werent any biases created by the selection process.
2. Although the study does show a clear (imo) difference between anti-RBA antibody concentration in infected vs vaccinated, it only shows this difference in the antibodies with the N501Y mutation. The study only examined one other mutation (WT) which was potent in its ACE2 binding capability, and doesnt compare any other mutations. Which brings me to my biggest issue:
3. This article was received on June 25, 2021, which means all of the antibody research was done before the Delta surge. We already know for a fact that there was a rise in breakthrough cases with the Delta variant, and research that Ive seen has indicates that Delta (and Omicron) use different RBA mutations to bind to ACE2 receptor.
Basically this study confirms what we already knew: the vaccine worked against the old strains of Covid, quite well. It unfortunately doesnt give us any information concerning the newest variants, or really any variants that dont rely on the N501Y mutation as a binder.