Generally, I track site resource usage using Google Analytics. Recently, I needed to check a clients site stats through AWStats instead. I noticed a number of URLs starting with /wp-json ...
My client uses FTP for a few web tasks and will not see those files in the directory structure. The fact that these record start with wp- is likely to be a source of confusion. While I understand that this is tied to the REST API in /wp-includes, I need to give my client a better explanation because I will be sharing those stats with her.