Note that the “5” in 5 over 1 refers to what building code is in effect for the floors on top, not the number of stories.
> 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
It’s true since the term became popular people have misunderstood, and it happens to match the number of permissible stories in current code, but that’s not what structural engineers meant when they started using the phrase.