simple explanation for beginners
Ethereum is the platform and Ether is the crypto-fuel or cryptocurrency that thrives over it. Ether is bought & sold and not Ethereum. Ethererum has various applications but Ether has only one application i.e. to enable operations on the blockchain.
Source:
coinsutra.com/ethereum-vs-etherI guess this is the
simplest explanation about the difference between Ethereum and Ether...

"To put it in the simplest of terms, Ethereum is a blockchain-based platform and Ether is the cryptocurrency that actually is the fuel of this blockchain based platform."
This is quotation from the article you shared with us. It's a great article and it explains
everything we need to know.
Ether is the fuel and it's what you need to have if you wish to do anything on this
chain. I think this little confusion is not a big deal, we can call this main token just
Ether, but in the same time we can call it Ethereum, it's the fuel and you can't do anything without a fuel.