They made a hypothesis and conducted a study to validate it. Perhaps they are wrong. Would be far from the first time studies are proven wrong. At least they did something. Make a better study. Make a hundred better studies. Prove them wrong!
The "Note that the senior author Bhattacharya and of course Ionnadis were advancing this theory before data collection began" is not. That's how science is done: you advance a theory, then you conduct experiments to validate / invalidate the theory.
I'm in no position to conduct studies, though I am certainly doing things in my wheelhouse to help. Other studies will clear up matters, but results may be weeks away. And these results may be used to end quarantines in the intervening time.
When people are strong advocates of a particular position, they tend to find ways to design or process experimental data in ways that support that position. The ways in which bias can seep into the experiment are not always easy for outsiders to see.
So it comes down to whether their "advancing this theory" went beyond what a reasonable scientist would do in postulating a hypothesis that needs testing.