A small, leaky skiff pulled up along side the boat, the man aboard having little knowledge of either the treasure, or robbery, going on aboard. He had just seen the ship not moving and, lacking a real ship himself at the moment, felt it his sworn duty to see if he could liberate these fools of theirs. He listened to the muffled speaking figuring there'd be no more than 2 on deck - now, this oversight and lack of awareness can likely be blamed on the not inconsiderable amount of rum he'd ingested as he pulled up, hoping to steady his hand, as it were. 
The effect was the same no matter how he missed it, and that was him being surprised as he leaped on deck, sword in one hand pistol in the other, only to see a much larger group than he anticipated.
"Alright, this it what we call....a..." His fearsome shout dwindled into nothing as the scene registered in his mind. 
"...Holdup."
Oh, crap.