oh wow, totally missed that
well good news is that SFEs (a pebble toothed eel) usually leave fish alone as their main diet consists of inverts like crabs and shrimp. that said, i have seen SFEs lunge at fish just for aggression (not to eat or kill), especially during feeding time. so have you kept your eel with other fish (specifically smaller fish)? were they ever attacked?
for a while, i would keep a close eye on the puff to see if it gets stressed or is attacked by the eel, especially when you feed them. should be okay though i think.