It's likely they have "whisperers" in games
While chatting in sofascore room you will find plenty of whisperers commenting live that this match is sold, X had sold this match to Y. But as soon as the results are near they are offline and we never hear from them. Frankly i would ignore such whisperers.
I also supported what you said because a strange don't worth to be trust cause they are the same as the online crypto traffic group which make false news in other to pump the price of their no potentials holding.
How come you have been trusted that random guy who whisper you. If the friend of OP had any sense and not listen to that stranger because probably that guy spy from other opponents and might wanted to fall in the trap and when having a bet.
Just focus your own bet, don't be distracted people around you you will not know who are they. And it should have a lookout behind you to prevent a scenario like that.