That's what I thought too. The definitions I found searching all say that any interview where you decide what to ask and how to interpret the results is "unstructured". The only "structured" interviews seem to be tests with pre-determined sets of questions, and the candidate's answers judged by formal criteria.

I'm not sure this division of the "interview-space" is all that useful. I would distinguish three categories:

1. You have an informat chat with me about the nature of the job, my experience, my previous employment, my claims about my aptitude, etc. Your impressions from this chat determine your judgement of my suitability for the job.
2. You ask me to answer questions or perform tasks that demonstrate my aptitude. It's up to you to choose the tasks, interpret my performance, and guide the whole process.
3. You give me a pre-determined set of questions/tasks that is the same for all candidates. My answers are mechanically interpreted by whether they coincide with the pre-determined set of correct answers.

If I interpret the definitions I could find correctly, 3 is a "structured" interview, and both 1 and 2 are "unstructured". To my mind, there's a world of difference between 1 and 2, however. 1 is of very limited utility (I want to say "next to worthless", but that'd be too presumptuous), and, quite possibly, does no better than deciding on the basis of the resume alone, thought I'd still want to see the data to be convinced. 2, when performed by a trained and calibrated interviewer, is - again, in my own experience - obviously superior both to 1 and to deciding on the basis of the resume alone. Maybe this is somehow unique to the profession I interview for, but I doubt it.

Suppose there's research which demonstrates that in some setting type 1 interviews are worse than using the resume alone. I don't know whether this is the case in the papers cited in this post (I couldn't read them), but I find it plausible. Suppose then that the conclusions drawn are the universal statements "unstructured interviews reliably degrade the decisions of gatekeepers" and "if you're hiring, you're probably better off not doing interviews". I consider such conclusions then to be obviously unsubstantiated, incredibly overreached, and highly dangerous advice.