Actually Silk Road is alive and well. It was shut down but it just came straight back it it still takes BTC. It was the original driving force for BTC and it still plays a part in it's demand. So no, it's not a joke and I intend to prove it this week when I cash in on this pattern.
it wasn't exactly the original reason. Silk Road played some part in one of the many price rises throughout the history of bitcoin and that part wasn't even the biggest part of all.
and also currently there are a lot more usages for bitcoin that any kind of usage of bitcoin in silk road or any other dark places of the internet is nothing in comparison.
and again also as some other user said, the days of people thinking bitcoin is anonymous are over. the awareness has increased and on top of that there are many good anonymous coins such as XMR which are being used. and that decreased the usage of bitcoin in silk road a lot.