Optimistic case:
A freak FUBAR of legacy systems, an unfortunate alignment of circumstances that could have happened anytime.
Pessimistic (paranoid) cases:
1. Intentional hacking by a foreign adversary 2. Vibe coding whoops 3. OpenAI agents "running experiments"
Any three of those pessimistic scenarios seem plausible though. Frightening. Intentional hack/exploit of air traffic control systems is the first thing that came to my mind when I first saw the news.