The author is claiming that between 1998 and 2010, managers earned between 379 billion in fees.
Generally, hedge funds operate on 2/20 model i.e. 2% of the assets as the management fee + 20% of the profits. [Obviously these varies across hedge fund but for now, let's assume everyone follows this model.]
E.g. If I give a hedge fund 100MM, they would charge me 2MM to manage it. Let's say they generate 10MM in profit. They will take 20% of that 10MM as performance fee. So to get 8MM, I will be paying them 2MM + 2M = 4MM which is 40% of the profits.
Now that's clear, let's run this logic on author's numbers.
Let's assume equal distribution which means that hedge fund earned around 30 billion in fees per year. (379 billion divided by 13 years between 1998 and 2010). If 30 billion is 2% of the assets, it means that they were managing 1500 billion dollars. The biggest hedge fund in the world, Bridgewater Associates, manages 125 billion dollars. There is no way other hedge funds can account for the remaining money.