That article doesn't provide a source or link to the study in question. All it does is link to a website that has been rated as having a conservative bias.

I'd be genuinely interested to read the study if you can provide it.

Edit: I decide to try and find it myself. Needless to say, there aren't any studies in the NEJM that support this claim with the confidence that the above comment suggests. However, this is the best guess as to the study in question: https://www.nejm.org/doi/full/10.1056/NEJMoa2119451

If you read through it, it does state that protection wanes significantly at 20 - 24 weeks (5 - 6 months), and this was already known. It does not, however, state that natural immunity is stronger or longer lasting than vaccination. It also states several times over that the results need to taken with caution and that more research will be needed.