First of all, this isn't really a "newbie" metar question.
CNVTV is the proper "contraction" for convective.
So, although what ERJ is saying makes sense, I'm not sure if it is completely correct.
I looked through all of the listed contractions and acronyms in the back of the Aviation WX Services Advisory Circular, and couldn't find the CVCTV.
Notice there is no AUTO in the metar, which means the person who manually entered the remark may have NOT used the standard FAA accepted contraction.
So then I would say that ERJ is right, their is some convective activity embedded in the clouds. This of course would have to be entered manually.