From the article: Our bread-and-butter living expenses are paid for by a single rental house we own, which generates about $25,000 per year after expenses.
One nit, perhaps, on that - is the rental house completely managed by someone else? If not, I assume there is at least some minimal amount of work associated with being a landlord... so I would hesitate to call him fully retired, such that he does not need to do any work for money.
The other thing I always think when I read articles such as this - if everyone took such advice and eschewed purchases (cars, lattes, drive-throughs, etc..), I would imagine unemployment would increase dramatically. However, it is safe to give such advice, because it is enough of a sacrifice / delayed satisfaction that it is unlikely to get enough people following the advice to negatively impact the economy. But someone needs to buy the stuff that is made, for the makers to have jobs!