Does my grandad know when he is going to die?

My grandad was diagnosed with stage 4 stomach cancer that has spread to his lungs and liver. He lives in a different country so any contact we've been having has been over the phone. He told my granny yesterday that he spoke to a fly and it told him he was going to die the day after tomorrow! Could it be the pain meds or does he really know, it breaks my heart that I can't be with them right now.