It does not need to be interpreted to observe the simple fact that it demonstrates, which is that the pressure in front of the fan is lower than the ambient pressure.
Once again, I don't think it is showing what you (and the chap in the video) think it is. Blow across a pipe and it will suck the air out.
Oh, absolutely it is showing what I think it is.
Last time I raised this issue you didn't catch on for whatever reason, so here's a video I just ran off to demonstrate:
I did catch on, and I gave the explanation.
That's an ally pipe with a plastic bag cellotaped on the end. The vacuum cleaner nozzle is actually the output of my vacuum, so blowing instead of sucking.
That's excellent that you did the experiment. Far better than drawing pictures and just imagining what will happen.
(FYI it's a DeWalt DC500 so not particularly strong, but I think we can agree that it is higher pressure than ambient and absolutely not a vacuum.)
No, I can't agree there, as you will see. It is actually a vacuum.
As you can see, blowing air across the pipe sucks air out of the bag, giving the exact same effect as the chap in your video.
How does he, and you, know that he is not recreating this situation?
Yes, I can see what you see, and here is the explanation.
Firstly, there is no such thing as "suction". Therefore, the pipe cannot suck air out of the bag. When we talk about suction this is just loose and imprecise terminology.
Gases (like air) consist of particles that are all pushing each other apart and trying to spread out. In the absence of overriding gravitational or accelerating fields, gases will spread out to evenly fill any container. The gas pushing against the walls of the container manifests as pressure, which can be measured. There is no such thing as "suction" because gases are pushing apart and trying to spread out, not pulling together. To have "suction" requires a "pull", which gases do not have.
Next, in the absence of gravity or acceleration, gases will flow from regions of higher pressure to regions of lower pressure. So we see, and can deduce, that the air flows out of the bag and through the pipe because the pressure inside the bag is higher than the pressure at the end of the pipe. The pressure in the bag is ambient pressure, and the pressure at the end of the pipe in the vacuum exhaust stream is less than ambient.
A follow on question is to ask, how, exactly, does a vacuum cleaner work? What basically happens here is that the motor creates low pressure inside the canister by "throwing" air out through the exhaust nozzle at high speed (it is a centrifugal blower). It works by catching air in the rotating blades, spinning it round really fast and throwing it out, much like you might get thrown off a roundabout if it is spinning fast and you let go.
By creating low pressure inside the canister, the high pressure atmosphere now pushes in through the vacuum nozzle to fill the void, and that is why the nozzle "sucks". But also, the low pressure air inside the canister is the same air the the blower is ejecting. This is partly why the stream of air coming out is at lower pressure than the surrounding air.
There are more technical details of course, but this is the gist of it.