In this industry something is bubble when it is about to drop, crash and go below the down trend line. Now since many years bitcoin has been on the verge of ups and downs due to its very much decentralised nature. This is the nature which can give fluctuations in the bitcoin market cap and its value as result of "no limitation on buying and selling as well". People go crazy about that all the time and when something really big bad ass happens then they panic sell like crazy and bitcoin starts dropping at alarming rate, now this is the period where people start using that Bitcoin is Bubble.   Isn't thats crazy. This is repeating since many years now and at each drop people are always there to call it as bubble.