the only thing that may add the edge is the knowledge that you have about the game you choose to play.
If that statement is directed toward gambling games then it's wrong because you don't get any edge over the house for any game that you play just because of the knowledge you have about it, that's now how gambling games work. I know there are a few games that might require your knowledge such as poker or blackjack, but even in those games, you need luck to be able to get good cards that you can use with your experience to win the games, but knowledge alone wouldn't make you win.
That statement can be correct about sports betting because it's the only part of gambling where your knowledge and experience are the most important things since you will need to have experience and knowledge about a sport and the teams involved to be able to make good predictions and get an edge over the sportsbook. Luck does play its role in sports betting as well but it's not completely dependent on that.
At least when it comes to poker you are not playing against the house and instead you are playing against other players, it is true the house gets part of each pot if you are playing in a poker cash game, but taking into account the service they are providing this is a fair trade, still it is true that even with the right knowledge it could be difficult to get an edge over the casinos as they have a whole team behind them while the gambler has no one to rely other than themselves.