It's only if something isn't as we assume (shower breaks, no eggs in the fridge, someone slams on the brakes in front of you) that we get in trouble.

Not all, only the impaired and unprepared :)

When an assumption fails, the prepared STOP

Stop Think Observe Plan

I heard it from some old white woman, who heard it from some bearded white guy , on the internet

That is right, when I am asked who I heard it from, humans want to know that someones status ( man/woman/race/age/bona fides)

Being a human, living with humans, I look at and remember faces, and with faces the information man/woman, color/race, hair, clothes....

So when someone calling themselves girl asks about drawing flowers, naturally we remember some girl , not some body

So some girl, I assume doesn't mean anything other than, it must be some human girl, don't know what she looks like or anything else about her.

It doesn't mean anything negative

All that psycho-knee-jerk-huu-haa is knee-jerk thoughtlessness, by jerks who assume calling a girl a girl is calling her bad at math, and other stupid things

You heard it from a dog