It is (nearly) impossible to find this page that documents the Random class by using the search feature. I’m assuming this is because the webpage in question is still hosted on the wiki.roblox.com domain instead of the www.robloxdev.com website.
When you search for random you get the following results, none of which are that I’m looking for:
There are also no references on other pages to that documentation as far as I know. The only way I know of to find the page is to search for the A Random Feature devforum topic and use the link there.