Well no, it says try to complete 12 and the difference is a common reason people stagnate in the gym.

It says to do only one set, lifting a weight heavy enough that you CAN’T lift it 12 times. The instruction is “once you can lift the weight 12 times increase the weight by 10%”

Many people go to the gym and pick a weight they can lift 3 sets of 12 reps and feel tired at the end. They then repeat this over and over very rarely increasing the weight because they still become very fatigued at the end of the 3x12. The articles recommendation may help some in that the notion of only having to do one set will make it easier to convince themselves to try a heavier weight, ignoring the temptation to “save themselves” for the next sets.

Scientifically most of the gains come from the first few repetitions, let alone sets. Although rarely recommended to beginners for safety reasons, and to athletes for specificity reasons, the most time effective protocol for muscle development is to lift a very heavy weight (5-6 rep max) only 3-4 times.