You may have left the site minutes ago — and yet here I am again: I've become your home page and your startup page. That's persistence.
When you clicked on "Add the extension", you installed what persists. A web page alone could never have done that.
chrome://extensionschrome://settings/searchchrome://settings/onStartup
In a real infection, it can also hide in policies
(chrome://policy), preference files (AppData),
modified .lnk shortcuts, or scheduled tasks.
Beyond the hijacking, see what a page can read as soon as you click "Allow" (files, clipboard, location, camera):
Click to cleanly remove the demo and restore everything:
If the button doesn't respond (extension not detected from this page), you
can always remove it via chrome://extensions.