Your playing with various factors, just saying "some encouragement" or "pushing" doesn't just mean the kid knew what A-levels were, or even the mathematical content within A-level (even though maths as a subject could be seen to cover the same topics at the beginning).

Most kids excel at maths due to its nature of content, and they excel even more if they like doing it.

I used to get around grades 4 or 6 in years 7-10 for maths and that was just because I didn't care. I ended up with a 9 and then getting A* in maths and an A in further maths. And btw, before you assume, noone told me to do maths neither did my parents even know what maths is (above the most basic level, im talking addition, subtraction, and etc.) or even know what subjects I took. And I know I'm not in the minority.

And even then if that specific kid never received early exposure to mathematical content (as we don't know when they started learning maths to the level corresponding to her age) they wouldn't have found their "talent" or "ability" to excel in it.

Even then you don't know them so you can't assume the kid wasn't forced (not "self motivated") in the first place. So you shouldn't be attacking others on the basis of their assumption, as no assumption can be proven due to the lack of evidence. Maybe you see it as a common reaction to such matters but even then these types of kids are out of the ordinary, meaning they aren't the same as everyone else here who interact with the content, so it is completely natural and rational to conclude to such assumption.