The OSD may not be the de-jure definition of "open source", but it is the de-facto definition. The statement above is correct in all but a trivial, pedantic sense.
Not just trivial and pedantic, this has been a common avenue of attack over the years in an attempt to dilute the meaning of the term. Such as when Microsoft made a concerted effort to try to redefine open source as "non commercial" source available software.