That's basically saying that it's sucking air from all directions, not predominantly from the direction the pipe is facing. Counterintuitive to say the least.
My understanding here is shallow, but I think you are correct.
Here's a simple exercise to help your intuition: open your hand up flat, and hold it facing your mouth, a few inches away. Blow, and you can easily feel the air pressing on your palm. Now inhale sharply; your hand will feel no suction at all.
That's true, but all the air molecules entering a tube aligned with X axis have negative momentum along X. You'd think this means the total X momentum of all molecules become more positive.
