"I always think of a crossover as something that produces seperated channels of a signal split into different bands of frequencies.. "
This is just what this does.

"Wouldn't using a low pass always result in the loss of the high frequencies and multiplying of the low frequencies.. "
Not if you invert the low pass audio & sum it with the original source. This creates something similar to a high pass.
If the chart doesn't make sense don't worry about it. You probably wont ever have the need for it then. This is why i made the VST plugin and Live preset. Much more user friendly.