State tax filing

How does "California Source" apply to stocks?

 

In the real estate example, it's possible to earn money in California even though you're in another state. Therefore, you could consider that a Californian source of income.

 

However, stocks aren't tied to an area. Let's say that I suffered a -$16 loss on a sale outside CA. How would I answer "Earned/Rec'd from CA Source as if Nonresident for Full Year"? Shouldn't I put $0 because, if I were a non-resident, then the sell would be a non-CA source?