This is not a stupid question at all. You would be surprised how many times we have people (or employees
) download the open source or pro version unintentionally and be confused by behavior as a result!
In any case, this command should get you sorted:
$ /opt/shiny-server/bin/shiny-server --version
Shiny Server (Commercial) v1.5.1.760
Node.js v6.9.1
If it has "Commercial" (or the similar command for RStudio Server says "Professional"), that means you should be good to go!! As you said, in this case, the server has been upgraded, and the open source version does not exist anymore 
If you don't see "Commercial" or "Professional," then you are probably using the open source version 
Let us know if that helps or if you have any further questions!!