This observation, borne out of my (admittedly brief) exposure to both hot air balloons (I know hot air balloon pilots and have ridden with them) and weather balloons (I planned, but did not execute, a project with my son's boy scout troop to launch a weather balloon to the stratosphere), combined with my engineering instincts (FWIW), convinced that the Wikipedia source was correct.
There are two mutually exclusive descriptions. JoeDaDude didn’t just uncover one but provided the reasoning why the second explanation is far more likely.
In other words they didn’t simply assert one over the other, but rather gave you the mechanism to say “oh you’re right” or alternately to point out the flaw in their reasoning.
I'm just looking at the pictures, but they don't look/lift like simple hot air balloons to me. I'd lean toward the science writer simplifying the language.
From TFA: "He instigated a top-secret experiment, code-named Project Mogul, that sent up hot air balloons equipped..."
I believe this is an error. Per Wikipedia [1]: "...rubber meteorological balloons, however, these were quickly replaced by enormous balloons made of polyethylene plastic. These were more durable, leaked less helium...". So the Project Mogul balloons were NOT hot air balloons. Which is not surprising. To fulfill the mission, a hot air balloon would have to carry fuel and perform controlled burns to maintain altitude. Not that this would be impossible, it is just easier IMHO to release ballast.
[1]. https://en.wikipedia.org/wiki/Project_Mogul