I would have never guessed people differentiate cousins so specifically
Oh they do.
In fact, the Romans had a different word for EVERY SINGLE RELATION based on closely-relatedness and parentage.
Mother's aunt, father's aunt.
Mother's mother, mother's father, mother's sister; all and more were completely different words.
As a not a native English speaker - what's a cross cousin?
As a native English speaker, I don't even know lol
Parallel cousins are your cousins from your mother's sisters and your father's brothers while cross cousins are your cousins from your mother's brothers and your father's sisters.
I understand what you're saying. However to me, whoever, probably from long ago, came up with this distinction makes zero sense.