I can't tell from the low res graphic if it's just a colored black and white, or a posterization. I'd assume the latter, just with more resolution to the posterization. Plenty of tutorials on it:
Edit: I played around with an image for a bit. I first converted to black and white - high contrast. Then did a hue adjustment layer, set to colorize, and picked my color. Then I posterized at a setting of 12-14 (on the base layer, so you can adjust your B&W, hue, and curves layers to get the look you want). Looks pretty similar.