Question about castellen’s “vehement aggression” rule

Reading rules for the black Templars’ castellan, and their vehement aggression rule is confusing me. Because you get to reroll failed hit rolls of 1 if you fail the leadership check, but get to “reroll the hit roll” if you pass. Normally I’d think it’s just reroll the entire batch of attacks, but the prelude to it makes it seem like it’s distributed on a model-by-model basis in the targeted unit. If anyone could help clarify this for me I’d appreciate it!