I regret being that loose with the designation :), Romanian and Hungarian are valid counter arguments.
In my mind, I was thinking of the belt of countries between Russia and Central Europe, starting from the Baltics down to the Balkan (excluding Greece).
Even by your definition, I can count at least seven countries where the official language is not Slavic. And that's not even including all the Altaic, Romance and other assortment of regional languages, many of which have some sort of official status.
Some of my fellow Romanians will also claim they're Central European, but in my mind, all the ones I listed are Eastern European countries. I'd even include Turkey and Kazakhstan in there, part of the latter is to the West of the Urals, which is what we normally consider the border between Europe and Asia.
That's cute. It is clear thats an outdated political organization and not geographical. Read at the groupings. Greece is more eastern than Albania (and it is one hour off timezone), and it says 'western' which is not the case by any geographic means.
Well, that and Romanian. And Hungarian. And outside the EU, Albanian. And Georgian, Azeri and Armenian if you consider those Eastern Europe.