The Sickness was a Nu-Metal album but I think the rest of their albums would be classified as hard rock. I wouldn't say they're Heavy Metal though, Heavy Metal is more like Lamb of God, Children of Bodom, Chimaira, Meshuggah,etc.
And when David said "hard rock/heavy metal show" I think he meant his band and maybe Lacuna Coil were hard rock, and KSE and Chimaira the heavy metal. Even though KSE is more metalcore. Disturbed is a little too melodic/slow paced to be heavy metal, which isn't a bad thing but just compare them to a band like Lamb of God and you'll notice the difference between the two genres lol.