Nope, don't think he was dumb, drunk, or a retard. If he was drunk he would have sobered up after a few miles and turned around to go home. He obviously admired his cousin, probably looked up to him. Wondered if he could do the same thing or was made of the same stuff. I wonder how long he was chewing on that? And how old the cousin was when he did it.
A man's got to know his limitations. Usually, that education comes the hard way. Luckily for him, he found out his were pretty close to his cousins. Now that this particular bucket list item is checked off, maybe he can move on to other issues he's dealing with.