No, I'm in the aquarium business, and I can say with certainty that this owner knew exactly what he was doing. By the time he released two adult snakeheads, he'd already fed them thousands of feeder goldfish. Snakeheads can be so mean they'll bite your hand if you put it in the tank. Most fish, including piranhas, won't.
Regulations for the importation of tropical fish vary, as is appropriate, from state to state, based on determinations of whether or not those fish might be a pest if released into the wild. There are a number of temperate and tropical species of snakehead, and I believe these specimens are among the former. Not sure if they are legal in Maryland or not.