So, we don't think the linux community and companies are much different from century-old business-process company with 1/3 million employees? Is this really a question, or just pedantry?
Silicon Valley is also huge old companies built with massive defence contracts. If you think Silicon Valley is mostly small startups you're mistaken.
When people refer to silicon valley, it is partially a reference to a place, but also partial a reference to simply culture.
Most people understand this, and quibbling over the exact physical location is just valueless pedantry, when the meaning was fully understandable.