One gallon of gasoline, properly applied, will move a 2,000 pound Volkswagen Beetle about 30 miles.
That's about the same weight and distance that a 16" gun on a battleship throws a single round that weighs about the same thing.
Gasoline is SUPPOSED TO EXPLODE, like pretty much all fuels.
Which is why there are even a couple of states in the US where it is illegal to pump your own gasoline into your car. No fooling, it is supposed to be too dangerous to allow drivers to do it themselves. That's what they claim and (ha) what government would lie about a thing like that?
Of course, we also have bans on cigarette smoking at gas stations, and somehow, a couple of folks set themselves and the stations on fire, each year, every year, while smoking at the same time that they are fueling. So who would expect boaters to be any smarter?
Seller was criminally negligent, buyer was...let's be kind and just say "uneducated". Sounds like a recipe for disaster. I'm not sure I'd like the alternative, which would be requiring "gasoline education and certification" before allowing anyone to buy, fuel, or operate any vehicle using it as a fuel.