Actually - that's a ref problem. Ref should have had coach removed player so game can continue. 15 minutes in a tournament game for U10 is at least 25% of match time. They received disqualification because it was against the rules and unethical. This is completely different from a team who has already won their previous 2 games and guaranteed a spot in the elimination round. Your comparing apples to oranges.
The question of whether something violates that the rules and whether something is unethical are technically 2 different things.
I agree they are apples to oranges, but this is NOT a ref problem. The ref can't order a coach to remove the player. If there's a suspicion that the player may have broken an ankle, the ref can't administer medical treatment by having the player removed. The coach can volunteer to remove the player (if he can be carried) but the ref can't order the coach to remove the player if there's a fear of serious injury (otherwise if there's any complication that's on the ref, who isn't qualified to determine how and when an injured player should be removed for fear of further aggravating the injury). The proper procedure if the player cannot move off and the coach will not move the player off is to call for an ambulance to treat and remove the player.
Since the game ended, there's not much the referee can do once the 3 whistles are blown other than note it in the match report. Since it is a violation of the rules (faking injury) disqualification is the proper remedy in response to this situation. This is an example of something which is both a violation of the rules and unethical. The "match fixing" situation was apparently not in violation of the tournament rules (there is an argument this fits in under the vague "disrespect of the game" rules, but it's hard to disqualify a team under such a vague standard, but the argument is whether it SHOULD be a violation) and there is an argument over whether it is or isn't ethical.