don't play the game myself but like most pvp games, you can use a 3rd party to bet on matches. either as a spectator or a participant. my understanding is that anything transferable is bet such as skins, weapons, pets/hats/other such stuff etc that you can get in game.
other possible answer here is the recent controversy with loot boxes you can buy with real money. since they are random items you get from the box, they have been classed as games of chance and labeled as basically in game gambling.
not sure which you are thinking of but there are the 2 ways i know of that games have been linked to "gambling"