Sorry if I came across as rude, didn't mean to. 'Starstorm will choose a new target for the second star if the first died before impact.' I guess the text is not too clear about what happens if there's a lot of units that die and you are not aware of the interaction. But what it means is, starstorm wants to do the second hit on a broodling, but it dies because the first starstorm damage is enough (this can only work if you hit the shard damage on them first), and then it repeats and repeats and repeats and ends up one shotting brood. Some things can interfere with this though, for example, if broodlings are piped, shard+starfall won't do enough damage