I wouldn't ignore the possibility of the lionfish being released from aquarium, as human stupidity is the most possible thing. However, I would say if the solution is to introduce another predator or another prey for the lionfish, it will screw up worse, covering mistake with another mistake.
How if earth is really changing?
I read before there are reports of finding animals migrating to unusual places, but I don't have time to gather the info now.
Everything is changing, weather, temperature etc.
Is it possible that the lionfish are naturally there eventually, migrate?
Earth used to thought as flat before it's proven to be round.
My opinion is just, killing doesn't sound like solving the root of the problem. It just scratches the surface and eventually problem will arise again, with more scars and bruises.