I very much doubt either. Lol. In my experience, it seems the more an individual progresses on the mystic path, the slower, softer, calmer, and spacey the music is preferred. I've also found in my observations over the last three years, that I'm not aware of any mystic who regularly attains 2nd jhana or higher, and at least one significant OOBE every month will have an affinity to lyric heavy music.
This makes sense to me, since lyrics are human concepts, and in those upper states the absence of human concepts is a significant relief and joy. Also, most lyrics are heavy with reference to worldly things--which is another quality a genuine mystic doesn't seem much interested in since the worldly is so unrefined and unsatisfactory. In my own case, after I had a few of these ecstasy (white wall of annihilation or samadhi 6 and higher) experiences, I lost almost any remaining affinity for lyrical music.
So, I doubt it was heavy metal

But I also think the type of music and how it's used is significant to whether it could be considered sensory indulgence. If it's worldly in nature as I described above, or it's enjoyed for aesthetic (5 sense) quality, then it's sensory indulgence. However, if the music induces or facilitates mystical phenomena, like a kundalini rising or spiritual/emotional cleansing, then it is not sensory indulgence.