Using the Web developer tools built into any web browser, you can edit the HTML of the page you are currently looking at, but that only affects what happens on your own computer, and it will all get reset if you just reload the page.
Actually, it is a very useful trick sometimes. I often do it when I am taking screen-grabs to go in a presentation, or if I want to mock-up some user-interface I am planning to implement.
But that could explain this screen-grab.
I am aware of the built in web developer tool. My best guess is the same. However it is very unlikely that our IT staff would do that as a prank because the screen grab was sent to our network team to highlight a potential of hacking of our Moodle site. But upon checking, we couldn't find the same image on the site and none of the Moodle file shown any sign that it has been modified.