As with most things involving lawyers there is a get out clause. Below I have capitalised the relevant bit from their policy

All partners, employees, contractors, clients, visitors and service providers ACCESSING OUR OFFFICES and events will need to be fully vaccinated against COVID-19, or have an accepted medical contraindication.

Just means that he can't go to their offices.

It's the same with my work. The government holds the threat of huge fines over my employer such that I cannot go into the office. My employer does not want to impose that restriction, but they are forced to.