Tell him life isn't over because he didn't make the team. I bet there's other programs outside of school that he can do track. It's reasonable he didn't make it. It's his first year in college, he's the new kid. You're not going to make any teams your first year in any type of school (Elementary, High, College, etc.). My brother tried to get on the basketball team his first year in high school and he didn't even make the first cut. He'd been playing basketball since he was six. Tell him there's always next year. And the truth is, there is next year. Why do we fall? To pick ourselves up.

Tell him to run for fun.

He is a lucky young man to have such a supportive grandmother and yes if he wants to make a career as a coach and a trainer it is especially important he overcomes this setback.

I suggest you remind him of all the athletes that don't make a team and use that to motivate them rather than destroy them.  Michael Jordan is a perfect example of using being cut from the varsity team that motivated him to work harder.

In our Mental Toughness Academy, we help athletes find a higher purpose in playing their sport rather than just winning or losing or making the varsity.  An example would be if following your faith is your higher purpose, then you would take this mistake as something that could strengthen your faith and know God's purpose is to teach you to overcome it and teach others.  

Your grandson's purpose could be learning how to overcome this so he could be an amazing coach, trainer and role model for the kids he coaches.