Ruby is a very durable and tough gemstone. However, its tenacity is still brittle, which means if enough pressure is applied it can crack or shatter. However this would have to be a very large amount of pressure for it to break due to its durability and is not likely, though still possible. It is more likely that the setting was not durable enough and too flexible or brittle itself. I would take the setting to a professional jewelery for analysis, or perhaps your insurance company can have it looked at by an expert to determine this.