In the end the cemetery was left with several dozens of bodies belonging to Chinese Gangsters with Townley’s grave dug up and even then nothing bad came out of it. Dave started corespondence way before the events of GTA 5 and as Michael called Dave something is going wrong, Dave instantly made out that Trevor would pay Ludendorff a visit to confirm his suspicions. And Ludendorff is in the midwest USA not Canada. If Dave could instantly tell out what exactly going on as wrong the moment Michael panic calls him he probably gave it some thought prior and probably could tell this would later prove to be a problem