It is meaning server-side dynamic content. That JS won't consume any noticeable CPU or RAM resource, it'll just be a static file pretty much always in memory, no templating engine in the web server process, no database hits, etc. All the significant processing load is either client-side or on another server (unless he is hosting his own analytics service), in fact the scripts are probably served by the analytics service servers too so even that miniscule impact is felt elsewhere.
The JS is not dynamic content as far as the WP server is concerned -- it's just a static JS file(s) that's served. The dynamic behavior it has happens (and impacts) the client (and whatever third party service does the tracking, e.g. GA).
3.3kb async loaded JavaScript actually. But the irony is not lost.