Beginners Luck occurs during the first few days, weeks or months of trading. Beginners are cautious and less greedy initially, they seem to be excited by a few stipend they get.
As I know, in trading luck is not the main factor for beginners or professionals. Because trading is an activity that must be based on skills and knowledge. If as you say beginners can make a profit for a few days or weeks or even months because they already understand the basics of trading and they enter at the right time with market conditions.
So beginners can make a profit not only because of luck but because the strategy and emotions they use are right for those conditions. However, in the next month of trading they experience losses, meaning their strategy is not working well or they cannot control their emotions in trading. So I conclude that beginner's luck at the beginning of trading is not superstition but because the strategy they use happens to be right. Because trading is difficult, it requires skills and strategies. So beginner's luck in trading as a superstition does not exist.