Technically, while still engaged in a match and having the system exit the game to ask you to either insert the disc or have the original owner log-in or to reconnect to Xbox Live for verification purposes, still ties into the direct definition of digital rights management, which is aimed to manage the digital rights of consumers using digital content. In simple terms, it's a security measure. Sadly, this doesn't exactly explain why it happened or what caused it. According to Arturo Sanchez, the event organizer and the one live-streaming the event when the incident involving DRM occurred, he's still baffled as to what happened, saying...
*Insert Tweet*
Someone tweeted him and mentioned that the game was downloaded to a second console and that's why it kicked them out, but it doesn't explain why it happened during the middle of the gameplay, nor why it didn't stop them from starting the game with a prompt on the dashboard, which is usually how most other forms of DRM work.
This is definitely a situation to keep an eye on as more details emerge.