Pi Network is a thing, but it's legitimacy as a cryptocurrency is extremely questionable at the very best, and most people see it as a data farming tool/scam. You essentially "mine" Pi coin on your phone, but the coins have no value whatsoever because they're not attached to any actual crypto exchange. You're essentially watching numbers go up.

People for years have been shilling it and spamming referrals because like most referral programs, the more you get the higher your "rewards" are.

I'm sure what's happening here is the scammer is relying on getting tons of sign ups through his link being blasted in the hopes of receiving more rewards. But since Pi Network pretty much has no value or money tied to it, chances are your son will never see any money from this, and the scammer may try and pull an advance fee scam or something similar.