Since crypto casino are provably fair, nobody has ever proved they could or were cheating on their customers to make them lose more often after they pass the beginners' stage. So, that is just a hypothesis, without further evidences to prove its point. I think it's just the nature of gambling games determined by an important factor, which is house edge. On short run (that is the period of time beginners make profit) it's likely gamblers make decent profit against the house, but the more they play, less likely it's going to remain the same, because inevitably the house edge will make total difference on outcomes, as it adds a slight advantage of 1%-2% for the casino. The percentage varies accordingly to the respective casino you are playing.
I suppose that is why we have the 'beginners' luck' phenomenon!
I believe that who ever wins in their first gamble game, was lucky at that moment, and was able to gamble on the right time of his luck. There is nothing attached to it. We know that gambling is more of luck than anything.
When I started gambling, my first game was in a traditional casino, and it was a game I love most and can play very well, so winning was cool and fun to me. Later on, I started losing and that was when I understood that it was not because I am very skilled in the game but I only need luck to win.
There are some people who think or say that a beginner in gambling will usually always be greeted by victory in the first session they do, but honestly I'm not sure about that, because after all gambling is still gambling, casinos never make anything (except luck) as a guarantee that someone including beginners will succeed in winning in their initial gambling session, In the end, it remains as you said that the victory that was achieved by beginners at the beginning of their gambling session was actually nothing more than a very lucky situation, or meaning that luck came at the right time and I am sure that there are some other beginners who have lost in their initial gambling session.
On the other hand what we must understand as gamblers especially beginners is that we must really understand that you will only be able to win when you are lucky, as you experienced in your gambling experience where you managed to win at the beginning of the involvement in gambling, I'm sure it was a pleasant situation but in the end you found out that the next session ended in defeat, which means that the casino does not make anything as a guarantee that you will win at the end of the session, it is still only luck that can ensure, while the name of luck is always unpredictable and this is the reason why all gamblers are always advised to gamble in moderation and put a budget that they can afford.