I know Dana Lewis, so I can probably tell you (the AC, not the reply) more about this system than the article does. There are safeguards around "use all its insulin at once" in the pump controller itself, that the OpenAPS system *cannot* override. The OpenAPS system effectively automates the "pushing the button" actions on the pump that are normally done manually by the patient who is reading his/her glucose meter and doing some fairly complicated math in his/her head to figure out the proper dose. It's an API client, nothing more.
The pump itself has safeguards against overdosing, either via manual control or APS control. And if there's a failure of the OpenAPS system, it simply reverts to manual control, which patients have been doing for years.