My brother, 21 yo, is like this. He’s ~180 cm tall and has never weighted more than 61 kg (during the 2020 covid lockdown, he made a big deal out of this since it was the first time he passed the 60 kg mark; after the lockdown was over he immediately dropped back to his perpetual weight of ~55kg). I live with him so I know his eating habits: he eats all the time, whatever he wants, whenever, how much he wants and simply doesn’t put on any weight. Is very energetic, no sick look / demeanour. It’s just fascinating to me cause I’m not like that at all, I have to watch what / how much / when I eat.
To chime in with the others and answer: hormones, activity levels, calorie intake. Those three give you your results. Hormones in particular will vary greatly and are influenced by activity levels but also by mental stress (or lack of), age, sex, environment variables such as temperature, etc.
As to why you didn’t get that bingo card- nobody has an answer really.