That's correct. The same sensor is used for both VOC and CO2. I asked the Footbot folks about the VOC/CO2 and how to obtain CO readings a few months ago and this was their response:
CO is included in VOC's measurements, so there's no reading you can get for it. Regarding VOC/CO2, there's no specific CO2 sensor as it's a value deducted from VOC measurements and complex algortihms. I must tell you that CO2 isn't a pollutant - if not in too much quantity - but is a confinement index. So when it rises, it simply means you need to open windows.
Not ideal, so if you want to dig deeper into VOCs you may have to combine the Foobot with some additional sensors.