"Fallfish" is Semotilus corporalis, which is a species of chub. Chub is a general name for a myriad of fish species, so if it falls into that general family or group, calling it a chub is not a misnomer, it's not as specific as "fallfish" or "white chub", but it's not incorrect. A creek chub and a fallfish are both species of chub, just different species.