Probably shouldn't tell border patrol you're doing unpaid labor in a country you're visiting. When speaking to authorities it's best to say the absolute minimum required for the encounter.
replies(4):
If there is ambiguity, then we can't have them here.
[1] https://marksgray.com/immigration-blog/can-foreign-nationals...
[2] https://internationalcenter.umich.edu/students/employment-vo...
[1] https://www.uscis.gov/policy-manual/volume-12-part-l-chapter...