I don’t know what could be your definition of fullness (everyone stops when their stomach gets completely full… Except maybe super extreme compulsive eaters who can eat even if it’s painful) but I can understand how odd it could be to stop before cleaning the plate just because you are satiated (or very satiated. really don’t know what your full means)!
It’s definitely a different feeling without all the interfering carbs for many of us. As I always could eat way over my needs with carbs, it was a welcome change when I just got a clear stop sign on carnivore (I didn’t have anything special on keto, just become able to eat at maintenance level but I had that before too, on low-carb). Food choices still matter, I can overeat like crazy without plants too but it’s significantly harder and most days are pretty okay.
I totally was the clean plate type but I don’t consider it bad at all. A plate is such a small amount (unless I am creative. one day I will test how big a plate I can make), eating some of it after satiation was usually okay with me. As a bigger satiation lasted more and easily meant less calories on average… But those times are over as I lost my ability to eat a ton more after satiation (without carbs or added fats, at least but I avoid those).
But I always was good at having not too much on my plate anyway. I used to have several courses and easily had 6 bowls of something (tiny bowls).
But not clearing our plate isn’t wasting… I put it into the fridge… I never ever ever ever would stand throwing out anything left on a plate, I saw it in shows and it’s so awful… It has nothing to do with anything (past, financial situation etc.) from my part (and my family’s when I was a kid), just Not. Wasting. Basic politeness especially in these modern times. So much energy and plastic and everything goes into our food and we are so many…
(I should think about it more and stop eating more I need then. I know. It’s not that easy all the time. Avoiding carbs and choosing good, satiating, protein rich food help the most.)
But no one in my family had that, ever… Looking at people they don’t seem hungry either. They eat. Our body recognize energy and uses it. Maybe not ideally with a bunch of carbs, I needed overeating but one can’t just stay hungry after eating not too badly (I mean, not low-protein, low-nutrient)…
Is it a HCLF stuff? I never knew anyone that had that weird style and I knew about it. Sometimes I wonder if I would be in constant hunger and misery on such a diet - probably not, I would find something. Even I know a few carby items with great satiating effect. Still would miss my fat and would feel in hell. I have nothing against that woe, each to their own but it’s horribly incompatible with me (and my whole family, I suppose. no one wishes to try it).