I am no expert but this quote is probably close to the truth. Losing weight is a science.This is nonsense. His problem as is always the case with someone carrying fat in their midsection, was insulin resistance. You don't need to go on a Keto diet to fix that.
He likely was making poor food choices relative to fixing his insulting resistance issue. The type of carb matters. If you eat high glycemic carbs and expect to lose weight, especially with an insulin resistance problem, you aren't going to be successful.
The real problem was he simply didn't understand the reason he was too heavy(outside of eating too much), and as such, solving problems without knowing what the problem actually is not usually very successful without a ton of trial and error.
There is no such thing as "I can't lose weight". Only that many people don't understand how the body works so their attempts to lose weight outside of cutting calories are poor at best.
A doctor friend that specializes in guiding people on ketogenic diets for weight loss told me if the person is not slimming down it is usually because they do periodic (or even daily) carb binges and they will hide it from the doctor.
I am only learning myself and the ketogenic diet has not yet slimmed down my belly fat which is my goal.
Learning a lot about insulin resistance and dietary guidelines is probably the key to stubborn weight loss.