Of course, it is a superstition plus luck.
I have some friends who bet for the first time and won huge during their beginner's betting, that's why we called it "beginner's luck" but still it will not apply to all. Luck is still your friend here even you are beginner or not.
That's why I don't believe on such superstition since see so many times newbie lose their money on their trades. Those immediate gain by other newbie is just part of their luck and this will not occur to other people.
Maybe they just buy that belief since some people want to attract new player and maybe take advantage of something they can get from those newbies. To lucky for your friend to win huge but what I really think those words said by people is just an expression for the winnings gotten by newbie people they know.
Let's assume a beginner enters into trading without knowledge and indeed most of them are not equipped with sufficient knowledge. So when they get a big profit from their first trade, then it is a stroke of luck. Why? because they entered the market without sufficient knowledge and without experience too. I think that is felt by some beginners who eventually think trading is easy, but they don't realize that they were just lucky at that time. However, not all beginner traders can feel this, it only happens to a few people. I remember some time ago my friend entered the market for the first time and they immediately felt a loss. So it was indeed because of luck.