That is right but when they use gambling as a hobby, they must thinks about the effects that they can gets from gambling. As playing gambling can gives them lose much money and the addiction, they must have a way to controls themselves so they will not lose that much money and still aware of playing gambling to avoids the addiction.
Not many people can wins from gambling so they must realizes about that and not using too much money to playing gambling. If they can control themselves when playing gambling, their risks to becomes addicted to gambling will not too big as they can holds themselves from playing gambling excessively. They will playing gambling for fun and can gives them relaxation and also peace of minds like you. But if they thinks that gambling can makes them gets deeper, they don't have to playing gambling and search for the other activities which will not makes them lose money.
In my opinion, if we talk strictly about the concept of “hobby,” there is still a difference between such hobbies as collecting stamps or baseball cards and such hobbies as gambling. This difference still manifests itself in relation to your passion for gambling. If previously unknown people find out that you are interested in collecting stamps, and this is your hobby, then the attitude towards such a hobby is still more favorable than if these people find out that your hobby is gambling. In the second case, strangers immediately develop some negativity towards this hobby of yours simply because gambling has long been classified as a wicked hobby.
By the way, all this must be taken into account when you tell strangers about your hobbies.
In my opinion, in terms of distinguishing or comparing whether gambling is a hobby or a hobby or not, I think it really depends on each person's point of view, but in simple terms maybe I would say from my point of view that gambling activities can indeed be as a hobby for someone but this is a very expensive and dangerous hobby, in the sense that when a hobby is like collecting stamps or baseball cards it means you have to spend money to buy the item but if you spend the money once you will definitely be able to get the item but in gambling you can spend much more money without getting anything.
This means that it can still be used as a hobby but with the caveat that it must be done with great care because there are very significant risks that can make us experience various bad impacts in life as we can see from what is experienced by gamblers who already addicted. And on the other hand, as you said, when we publish or tell other people that our hobby is gambling then maybe this information can trigger problems because overall gambling usually has a very negative stigma in the eyes of society which is caused by the large number of addicted gamblers who experience bad effects.