I find the article a little confusing. IMHO the point is that you must NEVER reuse an XOR key sequence for stream cipher encryption. With RC4, this meant that you could never use the same key. With modern stream ciphers there is the nonce for this - the CTR mode of a block cipher is also a stream cipher. (GCM mode is just an extension of CTR mode for authentication).
I've put together a little online demo tutorial (in my teaching and learning programming language).