Would they even notice it though? Normal bolides of similar energy happen fairly frequently (see https://catalog.data.gov/dataset/fireball-and-bolide-reports for an example). And even if they did, would they interpret it as a hostile act when similar events happen naturally without ill effect? It would mean the "attacker" posses the technology to accelerate materials to appreciable fractions of c while simultaneously not knowing that the impacts wouldn't do any damage to the target.
Should we similarly be afraid of making radio broadcasts lest our intended recipients interpret our beaming of energy as a hostile act? A somewhat similar concept is actually mentioned in the novel Blindsight. You could even go full Dark Forest and say that we're a threat simply by existing all the while brazenly advertising our presence through the oxygen in the atmosphere.
Should we similarly be afraid of making radio broadcasts lest our intended recipients interpret our beaming of energy as a hostile act? A somewhat similar concept is actually mentioned in the novel Blindsight. You could even go full Dark Forest and say that we're a threat simply by existing all the while brazenly advertising our presence through the oxygen in the atmosphere.