As you get older, you learn to concede to others accomplishments.
Yes, certain people will entice your competitive vigor and make you want to throwback even if just shedding some truths.
But try to take a step back. Are they hurting anyone? The group seems to be getting excited as him so let it go and let them. There is more to life than running.
Also, same applies for the other poster whose friend bragged on social media. You already did that when younger (presumably). I ran 6 minutes, 4 seconds in 6th grade (not that special but good). But they havent. Look at it not as a chance to prove world records are way faster but rather to empower them as humans. In my social circles, people who didnt run that are lacing up for race day or recapping, they will get an auto like from me on facebook because me being who I am (in their world the fastest kid in the school's history and a competitor on the state level) it encourages them.
So drop the hollier than though and encourage people.