this could end badly, page-25

Surly that is correct, but two things to note

1) Debt and IO are both USD so not all USD receipts will be able to be converted to AUD. I think the point you made is correct that opex is in AUD so they need to convert for expenses. However, they still have a USD interest payment to make so not all AUD improvement is realized.
2) When AUD drops is there a correlation to a fall in commodity prices, I will leave that one open.