The stark contrast between such a person and another that drives around in an air conditioned SUV is what often shocks people. By comparison, a western middle class person in India would be considered pretty well off! Unfortunately, the Indian upper middle class/upper class do not apply those standards to themselves.
There are some people commenting on this topic saying that SV millionaires are not upper class. That sounds ridiculous in India :)
Part of the issue is that lots of people talk about the USA being a "classless society". Some of them even believe it. More than most nations, America loves the idea that a person can arrive as a poor immigrant or be born the child of poor immigrants, apply uncommon drive and intelligence, and create a business that makes him extremely rich. (Whether that is the rule or the rare exception is another question.)
For example, if some, but not all (or even most), of your family members need to work in order to maintain a comfortable lifestyle (which includes healthy food, a home that is not crowded, access to decent education, and one to four vehicles) then you are middle class. If you have to work but don't have these things, then you are lower-income. If you can have these things without working at all in perpetuity, then you are well-off.