Level does mean brightness in the SwitchLevel context.
In HSL (what the labels inherited from ST imply but is not what Hubitat actually uses) and HSV (what Hubitat actually uses), the L or V terms actually are part of describing the color itself, regardless of the brightness setting. I learned this the hard way when I developed my own HSL and then HSV conversions before I knew that Hubitat had a built in conversion library. 
While I'm complaining, hue is on a 0-100 scale for no apparent reason, instead of 360 like it should be. The Hubitat conversion libraries already take this into account, so it only matters if you write your own.
Here are the definitions, from Wikipedia:
- In the HSV "hexcone" model, value is defined as the largest component of a color, our M above (fig. 12b). This places all three primaries, and also all of the "secondary colors"—cyan, yellow, and magenta—into a plane with white, forming a hexagonal pyramid out of the RGB cube.[10]
- In the HSL "bi-hexcone" model, lightness is defined as the average of the largest and smallest color components (fig. 12c), i.e. the mid-range of the RGB components. This definition also puts the primary and secondary colors into a plane, but a plane passing halfway between white and black. The resulting color solid is a double-cone similar to Ostwald's, shown above.[11]
