https://pmc.ncbi.nlm.nih.gov/articles/PMC7314691/figure/f002...

Take a look at their figure, especially in May 2020—the average appears lower, but, more significantly, there is much less variability in May 2020 compared to earlier years.

The authors' model quite strongly includes their preferred confound (secular decrease in PM2.5) but doesn't explore what other covariates could explain the differences between years.

It's fine to say that one should be skeptical, but one contrary report doesn't invalidate an antecedent report, and the structure of a linear model strongly influences an outcome.