What you flew through was not a CB.
The definition of a CB has been discussed at length on PPrune, for example
here.
If is was a shower, the existence of precipitation implies glaciation at the top of the cloud, which is probably enough to call it "cumulonimbus".
In practice, there's a continuous spectrum of cloud from little fair weather cumulus to the monstrous tropical cumulonimbus the everyone wants to be at least 50 miles from. The working definition among pilots of the difference between "cumulus" and "cumulonimbus" is that the line tends to be drawn by any given pilot at the size of cloud that she is not prepared to fly through.