While Krennic was the project lead before and during the events of Rogue One, Tarkin moved to assume command after the successful test firing on Jedah.
Supposedly, this image focuses on the loss of who would have been the presumed second in command / rival to Tarkin’s command of the Death Star project.
In either case, one could assume that the two characters would be sitting next to each other, out of deference for the chain of command.
However, there’s a key factor that could very easily debunk this rumor.