Almost nobody ends up with taxable income from renting because the rent goes to the mortgage, property tax, insurance, maintenance, etc.

Some of the highest grossing dividend stocks on the market are from REITs. Those dividends are coming from somewhere.

the part he’s leaving out is the equity he’s building at the tenant’s expense.

Sure. They're paying both the interest and the principle, and they're not seeing any of the appreciation of the underlying asset. I wouldn't even call this "at their expense" as there are some risk-benefits to renting (namely, no exposure to liability of the building loses value or falls apart). But its very obvious he's not suffering for this arrangement.

He's just not price gouging, either.

Which is probably the best case scenario in any kind of landlord-tenant relationship.