I mean, lots of fascists seem to like RATM because they never thought about the lyrics. I don't know if that phenomenon goes both ways, but I'd imagine there's probably at least one Neo-Nazi song out there with a slappin bass line. It probably mostly sounds like bad metal or generic 90s grunge if I had to guess, though.
I think the crux of the issue is that these people bought and supported the nazi bands by buying products on the website which is clearly a nazi website with clear nazi symbolism being displayed.
I wouldn't blame a rando not knowing they're a nazi band but if that rando actively buys from a site that has nazi symbolism and isn't hiding what it is then I'm a lil sus you know. At least I wouldn't support that sort of stuff once I became aware of it.