Sorry to hear about bumblebee.
Just a random thought tho. If the frog fish was swimming through rocks and crevices, it would be very hard for his tail to get caught if his full body fit through. The only way it could get caught would be a little land slide. Even so, the chances of of a land slide caused by him would be pretty low since they swim very weak.
I watched a bunch of videos on Lion Fish eating in the wild and in captivity, and I totally think a lion fish can rip off a tail no problem. A fin being bit off would be even easier. As for the clean bite, you said you came home to finding this. Which I'm guessing means you were out for quite a while. A series of bites can of the fin off then to the body of the fish can equal a clean bite. Cause as he the fins get nipped off theirs less of a fan to bite.
The lion fish's mouth is for sure big enough to take out the tail in a couple bites and a fin in even one. I couldn't find any pictures of a lion fish's teeth, but if its a carnivore then for sure it has teeth that can do damage.
Maybe you just don't wanna think its the lion fish because hes been eating and being nice to the frog fish; but if you watch a lion fish hunt, the fish around them aren't to worried about them coming close to them. The lion fish just slowly drifts to its position and gets really close, but the fish don't seem to care...and then he attacks. Its like it can change its mood without warning.