They talk about using them for delivery of harmless supplies, but I agree, as weapons delivery systems they seem to make more sense. They describe a balloon carrying up large numbers of small, largely transparent aerial vehicles that then drift to target locations up to 150km away automatically with a 1,4kg payload, then vaporize via sublimation and/or fracturing electronics to tiny bits from internal stresses. Why exactly couldn't these be carrying small shaped charges? And if they have a processor controlling the descent, then they could probably run at least simple image recognition algorithms, or even just IR seeking, once they get to their destination.
A 1,4kg shaped charge is no laughing matter - a mere 440g charge is said to be able to penetrate 35cm of armour. Even if the charge can't penetrate, say, tank primary armour, a precise delivery system could target things like optics systems, weapons systems, tracks, etc. Such a charge could completely take out unarmoured vehicles and would be particularly destructive to aircraft on the ground. Ammunition, fuel supplies, power substations, etc, etc... there's a lot of things a small explosive payload could take out. A balloon hauling dozens or even hundreds of them at once? You're basically talking "cluster cruise missiles". Carried on small transparent wings with almost no radar signature except for that of your munition.
I'm sure that these possibilities haven't passed over DARPA officials.