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.
Of course, bitcoin is not gambling but for those who are not yet aware about it they will think that bitcoin is a gambling.
Which they think are prices that go up and down to thousands of dollars a day, of course, like gambling, but this is common because bitcoin embraces a decentralized system so that prices are influenced by demand and stock.