From that link, it is not a treaty in US law. The article uses the blanket term "treaty-related law", but the Iran agreement falls under the "Executive agreemen

From that link, it is not a treaty in US law. The article uses the blanket term "treaty-related law", but the Iran agreement falls under the "Executive agreement" category. This is in part a long-standing presidential workaround for the similarly-long-standing Congressional unwillingness to bind the US to treaties. But it does come with a bit of deception of foreign partners, because it does not bind the US in the same way that treaties bind other countries under their own domestic law. One of many ways in which the US system is a bit dysfunctional.