https://books.google.com/ngrams/graph?content=design+system&...
Of course, there were systems in graphic design used earlier [1], but before 2016, the thing in the OP would be called "The US Web Design Patterns" or "...Language" or "...Toolkit" or "...Library", for the lack of a common term.
[1] http://assets.runemadsen.com/classes/programming-design-syst...
It doesn't seem super relevant whether or not there is a CSS/JS framework to support a design system — that seems more like an implementation detail.
And Brad Frost's Atomic Design [0], a formal system for developing a design system, was first written in 2013.
I you used that term in 2010, you are a real pioneer.
[1] https://twitter.com/search?q=(%23designsystem)%20until%3A201...