The article is implicitly asking you to make a small imaginative leap – that the bug expressed is in fact subtle enough it would have never been caught otherwis

The article is implicitly asking you to make a small imaginative leap – that the bug expressed is in fact subtle enough it would have never been caught otherwise – in the service of providing a concise, digestible example. It might have been better for the author to spell this out but I don't think it's really necessary.