But as far as I know it's wrong.
A one hour session of strength training will involve some amount of work, and a lot of rest. Compared to doing cardio, where an hour of work is an entire hour of elevated energy expenditure, you're effectively burning a lot less during strength training.
In addition, the "after burn" effect is very minor (in the extra tens of calories only range).
It wont make you loose weight however. It will likely make you gain weight as your muscles will grow. Which is explicit goal of many guys who start lifting weights.
When the gyms closed for the pandemic, I lost 5 kg of muscle. After coming back, I started doing fewer sets and have not regained the muscle mass. But my strength (the amount of weight I can lift) is now very close to pre-pandemic levels.
Most "standard adults" (e.g no injuries, obesity or illnesses) would not consider 20 lbs "difficult", to start with. And especially not after 6 months of regular practice.