What does he disagree with? I don't really think stopping smoking and weight loss is completely comparable.
Certainly with changing any habit there needs to be a mindset shift. I've never smoked so I've not had the experience of giving it up.
But with smoking, I think needs less frame of mind work to quit. There's all sorts of support available, and I get it's not as simple as 'you can just not buy fags' but well it helps doesn't it? If you don't have them, or the means to get them you can't smoke whether you're in the right frame of mind or not in that moment.
Whereas you can't not have food around - sure you avoid having crisps and chocolate in...unless others are having it for lunch. But that doesn't stop terrible portion control, or making the wrong choices for dinner.
Essentially, I feel with smoking it doesn't constantly require the right frame of mind, that you can put things in place to mitigate the times you lack willpower. That you can 'lapse' - that after you have one cigarette, you can quit straight after and that's that. Having 1 a week is better than 1 every 2 hours.
Whereas dieting, it feels like you have to constantly maintain the right mindset, you constantly have to choose one thing over another you might want more. You have to constantly deny every opportunity, and a lapse isn't just an end of a streak but actually sets you back, maybe not to the start but you have work to mitigate the damage, or repeat back through the progress you made, depending how you 'badly' you lapsed.