It's clear from the article that the amount of energy required for these bursts would be far in excess of what could be considered practical - even for planet-scope warfare. There is no characteristic gamma pulse which would be expected from an antimatter annihilation, and the pulse length is not exactly what we would expect from this type of weapon either.

But, as Udo kindly did, if we took it seriously, what would a civilisation have to do for us to detect its (warlike) actions and if we did, more importantly, would we believe it?