Article states that “…. the message triggered alarm bells after being picked up via Gatwick's Wi-Fi network”.
This doesn’t make sense. Snapchat doesn’t use E2E encryption for chats, but they do use TLS. So unless they got him to install a root CA onto his device (which I also don’t think would make a difference due to SSL pinning) I don’t believe this to be true.
Feels to me like he was either already being monitored by UK security services via a compromised device / the cooperation of Snapchat, or someone reported him.
Also, was this a bad idea and a tasteless joke, yes. But if all he did was send a bad joke to a private group of friends, I feel this is an overreaction and proof as to why we need E2E encryption widely.