PR people have been arguing about this forever. Online, stories are posted anytime, so the day of the week might not be that important. However, a lof of publications still have mid-week deadlines, which means that the reporter is likely going to be busier those days working on stories.
However, it's also interesting to note that the data in the above story is from when Crunchbase publishes a funding announcement, which is obviously 1-3 days after company sends out the press release. The author didn't really address that lag.
Still, interesting to read a data-driven analysis about public relations results.