He was probably getting at the fact you rarely see a black person in a heavy metal band. I can only think of 2 off the top of my head.
The thing is this is an entire band heavy metal band and there hasn't been many of those:
24-7 Spyz
A Band Called Pain
Black Death (American band)
Body Count
Fishbone
God Forbid
Living Colour
Sound Barrier
Unlocking the Truth
Wicked Wisdom
Wrust
As far as bands with black members there are quite a bit, most only listen to mainstream heavy metal though so don't know a lot:
Others (dead and alive)
Phil Lynott (Thin Lizzy)
Jimi Hendrix (Jimi Hendrix Experience)
Adam Warren (Oceana)
Lajon Witherspoon (Sevendust)
Byron Davis (God Forbid)
Tommy Vext (Divine Heresy)
Terrance Hobbs and Mike Smith (Suffocation)
Benji Webbe (Skindred)
Alexis Brown (Straight Line Stitch)
Derrick Green (Sepultura)
Tom Morello (Rage Against The Machine/AudioSlave)
Howard Jones (Killswitch Engage!)
H.R. (Bad Brains)
Vernon Reid (Living Colour)
Tosin Abasi (Animals As Leaders)
Rocky George and Eric Moore (Suicidal Tendencies)
Corey Glover (Living Colour)
Doug Pinnick (Kings X)
Slash (Guns and Roses, others, technically 1/2 black)
Pat Smear (Germs, Nirvana/Foo Fighters)