Well if bitcoin was a bubble... it is exploding now...!! just couple of months back it was hitting $20k mark. In start when it was going down every body was saying its going doing because of Christmas people are pulling out money for shopping but i guess they should have returned back... but they did not 
Look at the previous price drops. They have been much much bigger than this. I think this can be because of Chinese crackdown on bitcoin.
A single price drop does not mean that Bitcoin is a bubble. The drop in market cap is troubling though. And the fact that this drop has affected all cryptos not just Bitcoin.
Let's wait and see though. I think this Chinese crackdown is definitely bad news but Bitcoin can recover though.