It is not necessary for the air to move through the instrument. I have demonstrated this at clinics by having a tuba player blow smoke into his instrument. He can play for over a minute before any smoke begins to trickle out of the bell. Remember that this is a graph of pressure, not a picture of air movement. The nodal pattern is different for different notes, the number of nodes increasing with higher pitches.
Tubing is required to contain the vibrating air only at the pressure points.
When the G is played, the nodal pattern is such that a pressure point falls exactly at the place in the tube where the water key hole is located. When this key is opened, the hole in the pipe stops the tone. This fact is no surprise to anyone who has ever lost the cork on the water key. But when the C is played, the nodal pattern is different, and water key hole in the tubing comes at the taper-off of the pressure point. When E is played, the pattern is once again different.