Since I overheard you talking to that girl Aoko.
After hearing her birthday, you said yours was close.
Certainly, in France, ruby is the birthstone for March and sapphire for April,
but in America and Japan, ruby is the July birthstone and sapphire is September.
With a two-month difference, you couldn't really call them "close", could you?
And only in France is malachite the birthstone for December.
The two countries' stones are slightly different.
And that's how I figured it out.
You were French pretending to be American.