They're not, according to Japanese site RocketNews24. A Japanese traveler who recently visited the country and tried the dish said they're actually pretty good—and don't even taste like gasoline.
While Kotaku East does not recommend playing with gasoline or eating food covered in the flammable liquid, RocketNews provided a run-down on how to make the dish.
The clams were drenched in two 500ml plastic bottles of gas and then light ablaze. They burned for about five minutes and, according to the Japanese traveler, were some of the best clams he'd ever eaten. They were, however, slightly underdone.
Since raw clams can cause food poisoning, North Koreans tend to get liquored up on soju.
That's right, get liquored up and then bust out the gasoline and matches—which is sorta how Kim Jong-il ran the country.
北朝鮮でハマグリのガソリン焼きを食べてみた / 朝鮮人「たまに当たる人がいるけど焼酎飲めば大丈夫」 [RocketNews]