Is stack overflow reputation actually a Cryptocurrency? In a way, it is already a currency since I can offer a bounty for my question.

So is it correct to call reputation points from StackExchange a Cryptocurrency?

If not, then why?
No, it is not accurate to call the reputation system a cryptocurrency. 

Cryptocurrencies use a distributed form of updating the ledger of ownership, not controlled by any one person. Stack Exchange reputation points are just an online point system maintained and controlled by the Stack Exchange company. The two are very different. 

Cryptocurrencies also typically have a blockchain, and are transferrable at any time between any two persons. With SE Rep, you can only transfer if you do a bounty. And SE rep can be created out of thin air for someone answering a question well. Cryptocurrencies have a supply that is carefully controlled by code, and can only be created by solving a block.