Some relevant tweets:
The situation in a nutshell: Athena posts a picture of Brian’s board position after losing to him with her red-based strategy. He notably has two Circle of Protection: Red in play. People realize that his submitted “decklist”/picture of what he was playing only contains one Circle of Protection: Red. Brian won the event, but as the tweet above details, he returned the trophy after this information came to light.
This is arguably a watershed moment for the Old School community and format.