At most, it was a 'memorandum of understanding' between President Obama himself, and the other parties involved
Technically, yes.
Practically, no.
Every county that signed on to the agreement would be expecting the United States to live up to what was promised.
To other countries, which do not require their equivalent of Congress to ratify a treaty, this was in all essence, a treaty.
To them, Obama found a 'loophole' that bypassed the Congressional approval part.
Kudos to Mr. Trump for not caving to pressure. This was a major accomplishment.