Nitpick: the HTML4 spec was released in December 1997, and HTML4.01 only in December 1999 so it probably wouldn't have run in 1996s Netscape.
The doctype doesn’t matter in this context. Netscape Navigator 2 supported frames in 1995 and would render that page.
Back then it was common for Netscape to have features that (years) later became standard HTML.
The doctype doesn’t matter in this context. Netscape Navigator 2 supported frames in 1995 and would render that page.