For the record DD instructed me for my instructors course, so I can vouch for him being quite bright with a grasp of the technical aspects of aviation). Calibrated Airspeed (CAS), Corrected Airspeed (CAS) and Rectified Airspeed (RAS) are all different names for the same thing. So DD isn't particularly wrong, just perhaps could have phrased it a bit better.
It goes...
Groundspeed <--> (correct for wind) <--> True Airspeed
TAS <--> (correct for density) <--> Equivalent Airspeed
EAS <--> (correct for compressibility) <--> Calibrated Airspeed
CAS <--> (correct for position errors) <--> Indicated Airspeed (IAS)
At PPL level you are unlikely to be flying anything where compressibility is an issue, so you can assume that EAS=CAS, although technically that's untrue, and becomes an issue in an airliner or combat aircraft.
For most real-world operational purposes, you can also assume that IAS=CAS, although technically they can be as much as the greater of 5kts or 5% different.
G