Is Slipknot Metal

I posted a meme on r/MetalMemes that had to do with slipknot, the mods removed it saying that it wasn't about a metal band. I contacted them asking why they removed it, they responded saying slipknot wasn't a metal band. After that I told them that some of their songs were much heavier than most of Ghost's songs, Avenged Sevenfold's songs, and SOAD's songs. They told me that none of those bands were metal. So I came here to ask if the mods on r/MetalMemes are wrong or am I just stupid?