It depends on the gambler how he treats gambling. There are others who play for fun, so with this type of gambler, we can assume that gambling is a hobby for him, right?
But for a gambler whose aim is to make money, he/she cannot say that gambling is his hobby, especially if he already has an addiction to gambling that we know his body is looking for every day of his life.
If the player is trying to make a game with his work and it is unlikely that it will already be a hobby, but rather the main way of the ease. And a fool who really play for the sake of entertainment on weekends or with friends in some kind of short period can definitely be called a hobby in this case .
If both time and money are being controlled correctly it can treat as a hobby, though if the purpose is making money and being out of control then it might trigger addiction and may harm the person both financial and mental, more on self assessment and explanation if how they spend time and how they spend their finances, just like taking a movie night every sunday with budget that willing to spent, if there's no excess when playing gambling then can qualify as a hobby.
Yes, your opinion is correct, but overall, people who consider gambling as a hobby, in my opinion, must not be able to control both, namely time and money, because people who are crazy about gambling are crazy about everything, they can spend their time and money to be able to gamble, if they can't gamble, they will feel that something is missing in their daily life.