Ha, well it is a recreation and obviously not the original. They didn't have the original code so they had to work out how it was made. There's a readme which explains the process: https://www.microsoft.com/en-us/discover/1994/readme.html
Is microsoft.com currently not loading for anyone else? I'm getting ERR_SSL_UNRECOGNIZED_NAME_ALERT in Chrome, but I'm not seeing it mentioned anywhere else (e.g. Twitter).
Frames have been improved into iframe and then deprecated in HTML 5.
Frames were a nightmare. You can't link to a page in frames, you can't bookmark it either. Frames break the back button. Come in via search engine? You're only in the main frame, your navigation frame is missing. Want to print? Lol, good luck with that. You always ended up (either intentionally or unintentionally) with a browsing session within someone else's unrelated frameset.
Nitpick: iframes haven't been deprecated in HTML5. In fact they've been extended with new attributes like sandbox and srcdoc. Loading content via javascript is often a better approach but iframes allow you to sandbox content from your website's context, e.g. to prevent XSS attacks etc.