That's bad advice, especially with skim milk and bottled lemon juice. Other than being acidic, curdled milk bears no resemblance to buttermilk, and it cannot deliver the goods. It's akin to rice ...

Salt, citric acid, and bacterial cultures combine with skim milk and ferments for 14-16 hours. The sugars in the milk turn into lactic acid, which gives buttermilk its distinct tangy flavor.