Seems like they should have been on an L-B1 visa not a B1/B2 visa if that is what they were doing.
"The L-1B nonimmigrant classification enables a U.S. employer to transfer a professional employee with specialized knowledge relating to the organization’s interests from one of its affiliated foreign offices to one of its offices in the United States. This classification also enables a foreign company that does not yet have an affiliated U.S. office to send a specialized knowledge employee to the United States to help establish one."
"The L-1B nonimmigrant classification enables a U.S. employer to transfer a professional employee with specialized knowledge relating to the organization’s interests from one of its affiliated foreign offices to one of its offices in the United States. This classification also enables a foreign company that does not yet have an affiliated U.S. office to send a specialized knowledge employee to the United States to help establish one."
https://www.uscis.gov/working-in-the-united-states/temporary...