I worked as a temporary worker, helped people plant trees, had a rest after lunch, and my hand was broken. Is the boss responsible?

It's hard to say. It is reasonable to say that I fell during my lunch break, which is not a work-related injury. But considering that he fell down while eating at work (not at home), the boss should make some compensation. .

Article 11 Where a laborer suffers personal injury in employment activities, the employing unit shall be liable for compensation. If a third person other than the employment relationship causes personal injury to the laborer, the right holder of compensation may request the third person to bear the liability for compensation or the employer to bear the liability for compensation. After the employer assumes the liability for compensation, it may claim compensation from a third party.

If employees suffer personal injury due to production safety accidents in their business activities, and the employing unit or subcontracting unit knows or should know that the employing unit that accepts the contract or subcontracting business does not have the corresponding qualifications or conditions for production safety, it shall be jointly and severally liable for compensation with the employing unit.