Looking at the datasheet and pictures I think the heatsink is just aluminum. Looks like an extrusion (which means it's the same shape over the full length) with a solid center that they machine down in the middle area to mount the LEDs. The large amount of material and good conduction of the aluminum will absorb and distribute the heat without needing water cooling or heat pipes.

These LEDs use up to 200W and the heatsink on here probably weighs more than 10x as much as a heatsink on a 500+W graphics card. Watercooling and heat pipes are necessary when you need to get a lot of heat out with a minimum amount of material, such as for cars and home computers. Costs more than a big block of aluminum but the you don't need to move that much wieght around. For a light like this, the extra weight and space it takes up doesn't matter.