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.
As a newbie, losing money is only normal because they lack in skills yet but they only trade for experience to build their skills. And even for an experienced trader, losing is still there if all didn't go well. As long as there is no harm in superstition, then why not believe on them? Not all newbies are jumping in the water immediately but some do also make a research, so it is not only pure luck that made them earn their first few profits.
There is no way to tell if when luck will happen but one thing is for sure, and that is all of us must have our own kind of luck. I'm not saying that we will also proceed and copy those who only got lucky but of course, it is always better doing it in a skilful way.