A share goes to the members of that team. Members of another team, and wallets that only bought the coin, are outside this split. Joining the team on Pump.fun is what puts a wallet on the roster.
Pump.fun does not publish a membership API. Before a payout, Squads Cup records a snapshot of the team: the wallets, the moment it refers to, and the source of the list. The snapshot is reviewed before it can be used. Invalid addresses, program addresses and duplicates are rejected.
The payout receipt publishes that list and every amount. Open it and the shares of the included members match. SOL that arrives in the vault from anywhere other than the coin's creator fee is recorded separately and stays out of the automatic split.