In his video [Afroman] describes how the LM317 can be used to regulate current rather than voltage to provide a constant current source under varying load.

This is a very simple led constant current design using only 2 transistors, 2 resistors and an LED. This circuit allows you to use any voltage between 2V and 24V to drive almost any type of LED with ...

A current source provides electrical energy with a constant current. The implication is that if the resistance of the load changes the current source will vary the voltage to compensate.