Doesn't smell that bad.
If you read the account closely, it could well have happened the way that it was claimed. You have a man, retired USN, using his own name and the name of his boat (not an anonymous poster on a board) and the other boat, who would be putting his entire reputation on the line if he made up such a bogus story. Also, ultimately, the pirates would be out to board the boats, and according to the account, the victim only began to fire his shotgun when the pirates were attempting to board the boats. Yes, certainly, if these were "smart pirates" they could have done a lot better, but then, even here in the US, the criminals out there are not the brightest people around. And yes, though not in combat, I have fired all of the weapons mentioned, and am familiar with their capabilities.