The real-life issue is that it's unlikely that all things are going to be equal.And, all things being equal you get a slight bump in compression ratio when you increase the bore size
Replacement pistons are often sabotaged by reducing the compression height; AND the replacement head gaskets are generally thicker than the originals.
Unfortunately, "destroked" pistons are frightfully common in the aftermarket. You're lucky if you don't end up with LESS compression ratio; and what dicking with the compression height does to quench/squish should be a crime.
Now, if the oversized pistons have correct compression height, AND we're not talking about a Heron-head engine (a SBC is not Heron-headed; although the Chevy "W" block was) AND the head gaskets aren't thick as a feather pillow, then you're absolutely right--an overbored engine would have slightly higher compression ratio.
It's all dependent on the replacement parts selected.