It looks that way but I've seen him use that head a number of times and they're all exactly the same (apart from the thickness of the paint dulling the detail. At first I thought it was maybe a first edition daemonette with some horns grafted onto the top. I don't think it's from a citadel mini. - It appears that in the olden days the running of GW was a little more open to using parts of non gw minis in conversions. I assume John had carte 'blanche' in this regard...