Why does a query on a local instance with local database files cause NETWORK_IO waits?
Usually this surfaces as ASYNC_NETWORK_IO outside of Extended Events, but yes, it is the time SQL Server spent waiting for the caller (in this case SSMS) to consume the results. If the caller is slow (like SSMS) then SQL Server has to sit there and wait before feeding more rows. If you have a wide result set or large values, you should compare results to grid and results to text. But really, you shouldn't be timing anything based on response times in SSMS, since it does unrealistic things with the data and how it renders that your application won't be doing (hopefully).

I wrote about this wait type (and 9 other common ones) here:


What to do (or not do) about top wait stats