In the wake of the mass shooting at the Navy Yard in Washington, D.C. this morning, the Braves-Nationals game—to be played just blocks away—was canceled. It was a sensible decision that needed no explanation. Certainly not an odd one like "Postponed: Tragedy."
Usually, when a baseball game is postponed, it's due to weather, so you'll see a "PPD: Rain" notation or something similar next to it. For a short time—it's now been changed to merely "Postponed"—MLB's Gameday app followed this "postponement: cause" formula to the weird end you see above. It's obviously technically accurate, but more than a little strange to see it spelled out that way.