Yeah, that's roughly what I figured (IANAA). But it still seems hard to explain six flashes bright enough to appear like a supernova. I'd expect the flash of any kind of supernova to be brighter than the flash of a shockwave hitting a shell of gas. But I know nothing.

And anyway, for the shockwave from a supernova explosion to hit the shell of expanding gas from a previous explosion, that still seems to imply two supernova explosions from the same star. The only way I know that can happen is in a binary system.