First, you don't understand the methodology of this study. Difference in differences takes into account external events by assuming that two different time series are affected by external events in the same way. In this case, the two time series correspond to the number of views of Republican-leaning and Democrat-leaning users on X. Thus, the methodology takes into account external events.

Second, the speculation you're writing about is an interpretation of the new data analysis.

Third, the authors don't argue that correlation is causation. If you still think they do, then please quote the sentence where they do that.

Honestly, it looks like this thread is being taken down because some people don't like it, including you, which goes against HN guidelines.