A board member is not an employee. The term is commonly used for board members, officers, and directors of a company.

Install(v): place (someone) in a new position of authority, especially with ceremony.

At the level of average employees the company has all the power, but in the higher levels of corporate governance (the board) there is some element of pluralism. The design is set up to avoid autocrats, which is why CEOs can get fired.

Board members are not employees. Alford works for PayPal for example.

Install is a correct verb for board members and other high level executives, this isn’t unique to Facebook or even this decade.

It's a common English phrase. It just means he put them into place.