> the moralistic explanation
It is not a moralistic claim at all. Quite the opposite. It's a very common human struggle and to realise you are trapped in an addiction is the way to break free. Understanding that there it's something in the addictive substance that hooks humans, means it's not your fault. It lets you escape the crushing feelings of shame, blame and weakness. Better still, there are a lot of resources about recovering from addiction.
> "the inner food-addict concocting excuses for an XXL pizza"?
Ok so this is not a barb but jargon. Your inner-addict is a personification of the self-talk that tries to pull you back into an addiction. Your inner-addict is like the cartoon devil on your shoulder. You are not an addict anymore, but you still carry this annoying little inner-addict that you sometimes just have tell to shut the hell up.
For example, this little devil might be pestering you non-stop (what might be called 'food noise' these days) but the funnier aspect I wanted to reference is how your inner-addict comes up with the dumbest reasons to break your sobriety. These absurd reasons just pop in your head and if you are not paying enough attention, you might believe them. However if you manage to take a beat, you can realise it's the most laughably absurd nonsense but you were nearly tricked e.g. "I will never be a great writer if I don't smoke", "it's amazing how little I crave a donut, I should eat one just to prove how much I am not interested in them", "I should celebrate my 100 days sober with a cocktail!".
You can see how "I should get fat again to not be seen" has the suggestion of one these absurd justifications. If someone has lost a lot of weight they will have been through absolute hell with months of deprivation and struggle. It's a massive achievement. A rationalisation to excuse throwing away all that effort is insane but that is how addictions work.
> consistent with the notion from evolutionary theory
Ok, kind of funny. Evolutionary psychology suffers from "just-so-stories". It is possible to tell a nice story, but they have no epistemic value because there is no limit to the number of nice sounding stories and they are untestable. "Consistent with evolution" should only be said as a punchline. To be blunt, the story itself is speculative Freudian subconscious schlock which is why I believe I hear something similar from those fresh from therapy.