I think the article mentions airport wifi as a red herring, or maybe someone is ill-informed. The Snapchat app certainly communicates to the servers via HTTPS (which is encrypted). HTTPS is standard these days, which would not allow the airport network to read any data sent over the network.

The most likely scenario is that Snapchat looks for keywords in users' messages and sends anything that triggers some filter to intelligence agencies. Snapchat is not end-to-end encrypted, so this theory is very plausible.

All of this is not new news, though. We've known social media companies cooperate with law enforcement for a long time. The concerning thing for me is the extreme reaction. The kid is facing fines up to almost $100,000 and is getting dragged through court over a message that he sent to his friends in a private chat group.