Why is this so necessary currently? Nobody describes Einstein as a citizen scientist even when its main contributions were self funded. Describing Darwin, Mendel or Tesla as citizen scientists would be plain ridiculous. Science is not a religion, is a tool.
It’s pretty informal. I believe you’re reading too far into it.
Like most words it covers an inexact group of things often relevant to the context it’s used. From the context we can understand ‘citizen scientist’ to mean some curious old/young person in their garage (not literally always their garage) doing it for fun. Which itself doesn’t have to exclude the professionals with a side project.