Yeah, these AI detector tools are bad. (They also punish ESL as this tends to result in simpler language patterns that parse as LLM.)

The great thing about AI is that with a bit of imagination it can be used to amplify teachers too.

In this case, yes, you need to do a viva voce to convince the teacher (though I suspect they should be able to get fairly confident in 10-15 minutes).

But you could also have students convince an AI (probably in a proctored space?) if you need to scale this approach out.