You (and the grandparent) are misapplying the American conception of class (money) to a Briton. It's about birth and schooling here - money is irrelevant. The boy seems likely to be middle class. (Upper class means a member of the aristocracy in the UK, FWIW).
Yes, there are "several definitions" (as there are with most terms), but I'm talking about the normal and popular one - the one you'll find in contemporary and historical literature and on Wikipedia, etc. Here's wikipedia:
> The British "upper class" is statistically very small and consists of the peerage, gentry, and hereditary landowners. These people were traditionally the wealthiest in the land having inherited money and position. The majority of aristocratic families originated in the merchant class, and were ennobled between the 14th and 19th century.
Just as an aside - public schools like Eton were originally exclusively for the middle class (aristocrat children would have been privately tutored) and though since 1900 they have expanded in class terms to accommodate the Upper Classes (obviously including the Royal Family) there's no way a middle class person would feel out of place there.
