It seems to be context-dependent. I played in a brass band and they called me the string bass player. In an orchestra it's just a bass. I've played it a few times in my pub band, and they call it a double bass, probably to differentiate between it and the electric bass. Australians don't seem to refer to it as an upright bass, but maybe I haven't met the right musicians.
I think we should assert ourselves and just call it a bass. "I play bass."
As for the cello thing, well... There was this guy who once approached my band looking to become our manager. So he set up a meeting and was doing his spiel and then, suddenly, he said something like "You guys have a cello in your band. That's pretty cool!" Needless to say, he's not our manager.
Yamaha Club #247 | Eden WTDI Club #27