There is a difference between coming up with some way to adapt your dreams to the limits of your body versus what your initial comment which was simply "That guy could go snowboarding, he just thinks the warning he got creates a risk that isn't worth it."
I think people are entitled to decide the contours and priorities of their own dreams. If snowboarding was the author's main goal in life and "snowboarding" for him was a loosely-defined enough dream to still feel satisfied by whatever accommodations his knees forced upon him, then, yes, he could probably still reach it. But not all dreams are created equal and we don't have infinite agency. We have to pick our battles and the author may feel that while this is a dream, it's not an important enough one to go through all of the risks or other accommodations needed to get there.
Or perhaps his dream is to snowboard in a certain way, and have a certain kind of experience that simply won't work with his knees the way they are. I saw a video once of a guy carrying his brother who had cerebral palsy through a race. It had always been the brother's dream to race and since his disability prevented it, that was how they accomplished it. I am absolutely thrilled that both brothers were able to have an experience that feels so meaningful to them.
But, for me, if my dream were to run a race, being carried wouldn't feel like accomplishing that dream. Maybe another dream, equally worthwhile. But if it's not my feet pounding the pavement, that's not my dream. Perhaps the author's dream is similarly inflexible.
Either way, after someone writes an article about learning how to accept the limitations that life places on it, it seems rude to me to just tell him he didn't want it bad enough.