it's definitely ROCK/dead coral...live? now?...you can brush it/clean it, it will become 'live' in your tank, but something is causing the algae.
how long do you keep the lights on?
do you have a clean up crew?
New tank? cycled tank?
What makes rock live is not its physical form. It's the various life (bacteria, copepods, algae, sponges, worms etc.) on/in it that makes it live rock. Once you took it out of your tank it ceased to be live pretty quickly as the critters began to die off.
Your question indicates a basic lack of knowledge about this hobby. Do yourself a favor and read as much as you can either from books or this site or google things like 'live rock' and get a basic understanding. It will save you a lot of money and agony and make this a much more pleasant hobby.
I don't think he was trying to be a smart mouth. I actually think he was very nice about it. If you've had your tank up and running for 7 months and "have enough knowledge" than you would know that it is live rock. After 7 months in a tank a cinder block would be "live rock."
Maybe your question was misunderstood? What did you mean by is it live rock?