If I understand correctly this is the diff between two releases of this code, and we have no way of knowing what each checkin, including the culprit, actually l

If I understand correctly this is the diff between two releases of this code, and we have no way of knowing what each checkin, including the culprit, actually looked like. So even though at the two end points we see the addition of only one line in a block (which is being touted as the justification for this accusation), the intermediate steps could have included the addition and subtraction of other lines in that block. (A plausible example might be the addition of another hash updating if statement + goto fail, then the removal of only the if statement.)