Whoever quoted that google article hasn't read anything from the Bible. Satan was an angel. He could not create anything. He did not create sin either. The first sin was commited by Eve (and that is the reason why women have been considered inferior for such a long time).
Now, on to why masterbation is a sin. People had no idea what this white stuff was and went to the church for answers. In a quick spurt of holy-bullshit, they said "DEVIL FLUID!"
It does not say masterbating is a sin ONCE in the Bible. Don't listen to preachers, don't listen to other people. If you want answers about Christianity, read the Bible.
It really is a good fairy tale.