There is a "Hills" bias, but "Hills" doesn't necessarily equate to "mountains" in the map script. The thing to remember is that the map script engine is designed to only allow for one terrain bias type per Civ, so you can assign a Civ to bias towards (or against) a type of terrain (desert, grasslands, tundra, etc.) OR bias them towards coastal locations OR towards (or against) a terrain FEATURE (hills, jungle, forests, rivers). But you CANNOT combine any of those.
VP does combine a few of the starting biases for certain Civs (I guess because maybe one day we'll be able to figure out how to overwrite the map script hardcoding?), but only one actually takes affect. The order of operations is: 1) Coastal bias? 2) Terrain bias? 3) Feature bias?
So if the game code says a Civ has a "Coast" and "Hills" bias, only the Coast bias will take effect when the map is generated. Or if a Civ has a "Desert" and "River" bias only Desert will take effect.
The Inca's only bias is "Hills" but hills don't have to be near mountains and it's very map script dependent if there are even any large concentrations of mountains on the map at all. Songhai's only bias is "River" so it should always start adjacent to a river.