By common sense: most of academia is monetarily less attractive than Stanford Law School. The salaries of two full professors there make the family at least wealthy, i.e., able to maintain an upper class life. And the perks of being a full professor at Stanford Law School presumably include very attractive opportunities that can make one rich (able to amass wealth), e.g., well-paid consulting gigs and advisory roles.

But I agree, my distinction between wealthy and rich is pretty sloppy.