Assuming that the cabin crew started heating food as soon as possible after takeoff, 25 minutes into the flight could conceivably be the time it takes for the food heaters to reach high temperature. One (or more) of those food packages could have been a bomb - disguised as a meal (breakfast?) – detonated by being heated to a moderately high temperature.
According to passengers who flew with Metrojet in the past, no hot meals were served.