No, you're wrong. There are many, many species of beetles (thousands) that are called lightning bugs/fireflies. The terms are interchangeable, as they refer to any species in the entire family.
If it glows and it's a bug that flies, it's a lightning bug/firefly interchangeably where I grew up. I don't care if it has 8 legs, 6 legs, 3 body parts, or whatever. If it blinks in the dark and I could run around and catch it, maybe sometimes squish it and rub the glowy stuff on like war paint, then that's all that mattered. You sciencey types that like to argue on the interwebs are just weird no fun having fuddyduddies. =)