Hello, someone correct me if I'm wrong, I'm already a little late 1 year after the post was created, but even so I will answer, I think
that "it is more correct" to call it an opioid, rather than an opioid.
Opiates are the naturally occurring alkaloids present in opium, opioids are molecules "analogous" or with similar effects, the suffix "oid" refers to "similar to", as in the word "android" similar to man. I believe, and here I am speculating a bit, that to classify it as an opioid, they do not look so much at the structure of the molecule but rather on what receptors it acts on and the cascade of neurotransmitters it produces.
It sounds to me that there are several different receptors and not all of them cause narcotic effects. Without going any further, I believe that naloxone is also considered an opioid and I believe that it does not cause narcotic effects, on the contrary, it blocks the entry of other opioids, which is why it is used for overdoses, also methadone, which is used for detoxification and has no narcotic effects. I think yes painkillers.
Greetings
In the end it is just a label and it depends more on the receptors on which it acts and the neurotransmitter cascade than on the molecular structure