Dividends made sense 40 years ago as a relatively simple rule of thumb, but after all the work done by John Bogle with index investing, and academics with Monte Carlo sims and the 4% rule, dividend investing just isn’t the simplest, cleanest way to invest or receive passive income anymore. It’s actually significantly more risky compared to index investing, because dividend companies are a much smaller share of the total global economy compared to the broader indices.
If an investor puts $500,000 into a candy store with the agreement that the owners would pay the investor a percentage of earnings, that would be considered passive income as long as the investor does not participate in the operation of the business in any meaningful way other than placing the investment. The IRS states, however, that if the investor did help manage the company with the owners, the investor's income could be seen as active since the investor provided "material participation." 
I own several rental properties in the mid west and I live in CA. I have never even seen them in person. With good property management in place (not easy to find but possible) it is definitely possible to own cash flowing properties across the country. Not for everyone and not without it’s drawbacks, but it seems to be working for me so far. I’m happy to answer any questions about my experience with this type of investing.
One of the things I'm surprised your article doesn't mention is the tax advantages of this type of investment. The depreciation and rehab costs (purchasing distressed properties) can be huge deductions to ones income taxes, which none of the others have. Then, along with the appreciation of real estate, this passive income investment outperforms the notion of maxing out my 401k as well.
Residual income is the amount of net income generated in excess of the minimum rate of return. Residual income concepts have been used in a number of contexts, including as a measurement of internal corporate performance whereby a company's management team evaluates the return generated relative to the company's minimum required return. Alternatively, in personal finance, residual income is the level of income that an individual has after the deduction of all personal debts and expenses have been paid.