We have guns too.
You are right, and based on the photos that have been released and the many videos available on Youtube of what may be the very same boats, the US boats had overwhelming fire superiority. Does anybody really think a couple of guys in a plastic boat with AK-47s and one mounted 7.62mm machine gun would have engaged a US boat with multiple 50 caliber machine guns, M-240 machine guns, and a Dillon 7.62mm gatling gun? In the video below the boat has a remotely controlled 50 caliber machine gun with its associated targeting system. I'd rather not speculate about its performance, but I wouldn't be surprised if it is more accurate than a manually aimed gun. (Not all of the RCP boats are equipped with that gun system.)
Take a look at the live fire drill here
Interestingly, in the DOD released videos of these boats training near Bahrain, the crew also carry rifles, so even in a close quarters battle they have an extra weapon.
Someday we'll learn the real story.