No. It means that the virus that turns people into zombies has tried out a bunch of different tactics to spread, and it found that the one that causes a large AOE attack causes the most people to die.
Only if the zombies are created by a parasite or disease. If they are artificially created by a necromancer, it simply implies that the necromancer has a use for exploding zombies.
Okay, but in that scenario, it's not really a case of the zombies being an intelligent, self-reliant militia; more so, mindless drones that have an intelligent leader.