Sitemap vs Hierarchy chart

I'm new to UX and am confused and cannot differentiate between a site map and a Hierarchy chart.

Logically I understand that a hierarchy chart is a general name and the site map is a specification related specifically to websites.

But someone I know who teaches UX, claims that they are two very separate things; according to her the hierarchy map describes the navigation process whilst the sitemap is a representative structure of the web pages for the whole website that doesn't show the linkage between the webpages, rather just shows the hierarchy regarding the information in the website.

Can someone please clarify things for me?