Looks like while some people agree with you, it's not the most common use.

> The name derives from the maximum permissible five floors of combustible construction (Type III or Type V) over a fire-resistive Type I podium of one floor for "5-over-1" or two floors for "5-over-2", as defined in the United States-based International Building Code (IBC) Section 510.2.[1][4] Some sources instead attribute the name to the wood framing of the upper construction; the International Building Code uses "Type V" to refer to non-fireproof structures, including those framed with dimensional lumber

https://en.wikipedia.org/wiki/5-over-1

It’s debated, but the prevailing belief is that it originated to refer to the number of stories. Hence you’ll also see “5-over-2” used fairy commonly as well.