Vesper wasn't a mind reader. She used her intuition to size him up.
Her usage of "Oxford" and "Rolex" was meant to convey a type of education (prestige) and watch (luxuary/expensive), which applied to Bond since his education consisted of the prestigious "Eton" and "Fettes" and the expensive watch Omega.
It would have been shoddy writing had she said Eton and Omega.
No it would not have. Eton sends a very different signal than Oxford does.
Eton is perceived as being an upper-class institution; Oxford is as well but much less so. Most Oxonians I know are slobs - most Old Etonians I know were taught to dress properly.
Oxford's prestige is as an educational facility; Eton's is of an educational and social facility.
Vesper confused him from another Bond who took Oriental languages and brushed up on a bit of Danish at Oxford.
That (Oriental Languages) was at Cambridge.