That's only true if you're looking at the overall cost vs. investment profile, but I'm not entirely sure that's the point.

Renting out a property that you own can still be a long-term beneficial investment so long as the rental costs exceed the costs of borrowing on a mortgage – and that's typically much, much lower than the value of the actual mortgage payments being made. Capital growth potential is a valid reason that people may choose to invest in property, and in a market where there are many rental properties to choose from it's quite possible that rents remain below the prevailing capital repayment + interest that a mortgage would require.

But really it's hard to understand exactly what the point being made in this article is – it seems to be primarily that the "total amount" of rent being paid is now approaching parity with the "total amount" of payments being made by homeowners. I can't tell if that includes capital repayments, or if it's even accounting for an increase in renters vs. homeowners. There's basically no useful information there.