That's nonsense, and taking one look at basically any fund manager will tell you otherwise. Just to give the most outrageous counterexample, the sovereign wealth fund of Norway employs 550 people and manages $1 trillion in assets, including 1.3% of all global stocks.
Given the content of the link nikanj provided, it makes more sense to interpret “Takes a lot of people to manage that much money,” not literally, but rather as meaning “Takes a lot of people to run an organization that big.”
From the link:
In 2017–18, Stanford is a $6.3 billion enterprise. This figure represents the university’s consolidated budget for operations, a compilation of all annual operating and restricted budgets that support teaching, scholarship and research, including the budgets of all schools and administrative areas and the SLAC National Accelerator Laboratory. It does not include the $1 billion capital budget and excludes the budget for Stanford Health Care and Lucile Packard Children’s Hospital.
https://www.nbim.no/en/organisation/about-us/