I think if you call it just “an experience” is kinda undersells mate. it not seems anything harmless to me, although he didnt spent too much time on it but it seems very serious gambling disorder to me even more than sports betting/casino betting, spacially when he is very young guy. seems it is no longer at that level, like just a lesson learned, real harm is awaiting. Yeah you could say he is no longer in it quitting is huge however such shit runs deep. i think this friend could not go through a learning curve, he really needs tools maybe therapy or support group.
I have suffered from addiction and know what it means to have little or no control over an activity. Some people are not strong enough to overcome this abnormal behaviour without help. I was able to break free through meditation, reading, and watching videos on YouTube. Your friend needs help, and you can assist him.
The first step is for him to realise that he has a problem and is willing to seek help. These days you can access almost every service on the internet. If he is too shy to visit a local therapist, he could seek help online..