You cannot say they were lucky after hundreds or even thousands of bets, because no one is that lucky, it is clear they have a system that can give them profits and that is why they share their tips but not the mechanics behind their system.
The only winning system they can ever have is knowing when to quit when they already one, other than that there are really no proven system or trick in betting in which you are set to win everytime you bet. Gambling even if you have the upper hand on bets is still based on luck and sometimes being in the upper hand is not always gonna turn into a positive outcome. If there is one, I don't think the gambling sites will be happy and they will probably change their game if they found out that they are in a disadvantage.