Explosions are very possible while fueling a boat. That's why all hatches/doors/windows should be closed while the gas is pumped (to prevent gas vapors from collecting below deck). Blowers to engine compartment must be run for several minutes before every launch, and the compartment should be checked for fumes before getting underway. Around where I live there's at least one boat every year involved in one of these explosions, and it's because inexperienced boaters think that, as with their cars, boating is just a matter of turning the key and heading out.

These poor people had only taken possession of the boat the day before this tragic accident occurred. They couldn't have been very familiar with the boat and it's very likely they hadn't gotten around to educating themselves on basic boating safety either. Very sad.