What UB? This has nothing to do with UB; it'd be well-defined in any language. It's equivalent to this python snippet:

  config = load_config()
  if !config.valid():
    sys.exit(1)  # config is corrupt. restart pod

Did Python do something wrong by letting users call `sys.exit`? No. This is a deliberate crash. Under other circumstances, crashing might have been a valid strategy, but here it turned out to be a bad choice, since Cloudflare's infrastructure was restarting the service with the same bad config every time.