25,000 feet v 40,000 feet
In fact the same article states that pressurised breathing is only required over 40,000 feet:
Oxygen Delivery Systems
Continuous flow.
This system delivers a continuous flow of oxygen from the storage
container. It is a very economical system in that it doesn’t need complicated masks
or regulators to function. But it is also very wasteful—the flow of oxygen is constant
whether you’re inhaling, exhaling, or pausing in between breaths. This system is typically
used at 28,000 feet and lower.
Diluter demand.
The diluter demand system is designed to compensate for the short-comings of the continuous-
flow system. It gives the user oxygen on-demand (during inhalation) and stops the flow when the demand ceases (during exhalation). This helps conserve oxygen. Additionally, the incoming oxygen is diluted with cabin air and provides the proper percentage of oxygen, depending on the altitude. This system is typically used at altitudes up to 40,000 feet.
Pressure demand.
This system provides oxygen under positive pressure. Positive pressure is a forceful oxygen flow that is intended to slightly over-inflate the lungs. This will, in a sense, pressurize the lungs to a lower altitude, thus allowing you to fly at altitudes above 40,000 feet, where 100%
oxygen without positive pressure will not suffice.