It's not checking you against a sexism filter - it is subtly pointing out the pervasive gender assumptions society has.
It's in all likelihood an innocent mistake on your side - but the accumulation of those tiny things is, in the long run, "not fun"(tm). It doesn't matter that they're innocent mistakes, it matters that it is a constant thing.
So, please, don't consider this an attack, but a polite request to double-check the next time you make a gendered reference to somebody. Every time you do check, you'll have made life a tiny bit better for the women in the field.
It's in all likelihood an innocent mistake on your side - but the accumulation of those tiny things is, in the long run, "not fun"(tm). It doesn't matter that they're innocent mistakes, it matters that it is a constant thing.
So, please, don't consider this an attack, but a polite request to double-check the next time you make a gendered reference to somebody. Every time you do check, you'll have made life a tiny bit better for the women in the field.