I don't know why people say bitcoin is gambling. Its not gambling. You are investing your money and time. You use your internet. So its not gambling dealing with it.
Bitcoin can also be called gambling. If it raises you have money. If the price drops you lose money. But if you dig a bitcoin. that is the property. You bring bitcoin to exchange or buy -> it is currency
The two concepts are getting confused among the users. There are some people who use Bitcoins for the sake of gambling and hence it has become a myth now that Bitcoins themselves are a form of gambling.
Gambling is totally dependent upon the luck and does not require any effort whereas the Bitcoin mining, trading and all other matter do involve a lot of hard work. Therefore it is not worth stating that Bitcoins are a type of gambling.