This paragraph is taken from theJames Hardie website.....
HardieBacker® 500 Cement Board for walls and floors delivers superior protection against moisture damage and mold growth. It contains no paper facing, which serves as a food source for mold, or gypsum, which can disintegrate with continuous moisture exposure. HardieBacker board is an ideal choice for wet area walls; its smooth surface may be painted, textured, wallpapered, or tiled. HardieBacker® 500 board is available in a 3´x 5´ and 4´x 8´ sheet size and is backed by a limited lifetime product warranty.
I agree it should really be used as a tilebacker but their own website says it can be finished in other ways. I wouldn't recommend it myself either.