TLDR; No. Even the context (language or language-specific platform) can be used interchangably, codes mentioned here generally tend to be maintained on GitHub or npm for Javascript (so again it can be linked to a repository on GitHub or on some other platform).
Clarification:
First, clarifying the name of these scopes you mentioned above like, design system and Javascript framework will be more appropriate. Even there is nothing stated with 'import ...' with the link you provided, you probably meant the imports alongside with this link (Please warn me to edit my answer if it's not the case).
Explanation:
Well import
is widely used in many programming languages (even sometimes in an alternative form), here with the link, it's both used in css pre-processor and for frameworks like React and Vue as well. So that yes, they're mainly used within files related to that specific code platform to be included in programming context.
And for your consequent questions, these import statements preferably used on that specific part of the project page, like component mentality as almost the same with design systems. For more appropriate words, it allows users to import whatever part of this library or design system instead of copying all of these features of that specific content within the imported file scope.
Extra Info:
Also as you mentioned with your question, it's not something necessarily displayed on that page for live demo
purposes. Basically apart from the webpage it's displayed, for Javascript packages i.e., the library stays on npm
and when it's imported, it directly comes from another source (that's the code repository). So that even you copy this statement from the displayed webpage, there's no direct connection between these sources and the user should install these libraries as well beforehand in order to successfully importing these libraries.
Lastly, there's a good usage of both the design and code displanation within the same place with Vuetify library, works like a plugin to Vue framework you mentioned. Hope the answer helps and please don't hesitate to edit your question to let me edit mine, or comment as wishing me to explain more.
Note:
The Javascript frameworks you mentioned above (namely React and Vue), are not design systems but more of that, they're the technological background for these design systems are used on. But the repositories like Vuetify or more popularly Bootstrap, are a kind of tools including the features like letting their users to shape their application via code, so that can be understood more close to the design system in this context. Hovewer, besides having also more capability then design systems, seperately they can be used to designing an interface with lots of ready-to-use components, giving proper functionality with a shorter code to be executed by users, or even letting their users to be able to work with test frameworks within these libraries' components or functionalities.