Other mistake: Commissioner Selwyn Patterson puts some pressure on Humphrey and the team saying that "a wealthy tourist has just been killed." But Dan Hagen was not a tourist; he lived on Saint Marie with his wife, as said by the fellow oceanographer Jonathan Taylor, and they have a villa. Someone as well connected and nosy as Patterson wouldn't miss the notion of a multimillionaire living on the island. He also says that he needs to reassure the yacht club that there are no pirates in the area, but it was already established by the coast guard that no ships approached the area. (00:12:15)
Other mistake: It's played as a gag, but still it's quite inconceivable that in "fifteen minutes" it would get pitch dark so that Dwayne can avoid his duties sanding the ship! How much time could he have bought even if he had more excuses up his sleeve? Goodman really can't tell the difference between 15 minutes and a couple of hours? The scene started when it was nowhere near dawn. (00:21:10)
Answer: Most likely they had only tropical exotic drinks, he wanted an old fashioned English beer.