[m1el]

You're correct to have a suspicion here. Hypothetically the explainer could omit a neuron or give a wrong explanation for the role of a neuron. Imagine you're trying to understand a neural network, and you spend enormous amount of time generating hypotheses and validating them. Well the explainer might give you 90% correct hypotheses, it means you have 10 times less work to produce hypotheses. So if you have a solid way of testing an explanation, even if the explainer is evil, it's still useful.