Is there a Blockchain per bitcoin wallet? According to this article "A gentle introduction to bitcoin", it looks like a blockchain is created per Wallet. 

Is this correct or am I misunderstanding it? If my assumption is not correct, what determines when to create a Blockchain?
"The blockchain" is the universal list of all Bitcoin transactions that have ever been confirmed.

A new wallet doesn't "create" a new blockchain.  Rather, it downloads a copy of the existing universal blockchain.  It does create some new files on its own computer to store the data it downloaded, but the data itself isn't new.

(This assumes it is a "full node" wallet.  "Thin" or SPV wallets don't download it; they rely on other nodes to tell them what transactions already exist.)