Fish jump all the time. I think we've all lost a fish to "carpet surfing" at one time or another. Sometimes the lights turning on or off can scare them, especially if they are new to the tank. Sounds like that may have happened in your situation.
I would be hesitant to say that fish jump because water parameters are off... They jump out of perfectly healthy tanks all the time. Fact is, they get spooked easily. And in the ocean, they can swim upwards or jump all they want and nothing bad is going to happen to them. Maybe they just don't know it's bad for them ;)
You can buy eggcrate (sold in the lighting department, also called light diffusing grid) at Home Depot or Lowe's. Cut it to fit the top of your tank. That works to keep most (but not all) jumpers in.
Lastly, some species are more prone to jumping than others. Almost everyone that's ever had a goby or wrasse has had those fish jump. It's just what they do.