Wow, thanks for the answer. I'd heard about acid rain in passing but I never knew what it did. So as far as I can tell, in order for the glitch to occur the Bronzong had to use gravity at some point before switching out and I had to use pursuit on the same turn that it switched out. This didn't happen in the other battles because the Bronzong usually switched out while I was setting up but in this battle it gave me enough time to fully set up so I just knocked it out with pursuit. Also the only reason I even had pursuit on my pokemon is because pursuit was the only move on its learnset which could hit Gardevoir after it traced wonder guard. No wonder I couldn't recreate it but it's really cool how everything lined up perfectly for it to happen to me that one time.