Your link is about comparing index funds with people who manage other funds. None of these people are involved in the business operations. So yes, they suck and index funds do better. The investments I am talking about are where you invest directly in a business. You are not buying stocks in the business, the value of which depends on a fickle market (hence why I explicitly said "non-publicly traded investments"). You are buying equity of the actual business, with a contracted amount of returns (i.e. preferred investor). The operators I spoke of are the people who are actually running the business. In the case of an apartment complex, they are involved in the operations of running the complex.[1]
Don't think in terms of the stock market and index funds. Think in terms of "Hey, I'm starting a business and I'll give you 3% of equity if you give me $50K." The difference is that here they typically aren't starting a business, but buying an existing business (that already has clients, and a revenue history), so it's easy to analyze whether the business will be successful, and get a good forecast of revenue in the first 5 years.
For the record, most of my investments are in index funds so I know where you're coming from.
[1] OK, not really. Most will hand off to a property management company, but they've vetted the PMC before offering the investment to you.