You are correct. Players don’t get to make official rulings. In my opinion, now knowing all the details, you made the correct ruling.
That being said, if all the players in the group discussed without a consulting a TD, and told the player “Hey, we’ll give you a comp ball if it drains both,” there’s no way for you to stop something like that without your knowledge as a TD. And they may have all been good sports and followed through on what they told the player. However, if one of them decided to renege on what they said and once the natural 3-ball game was over, told the player that they don’t get a comp ball, then as a TD, you must take the scores as reported on the display, and no comp ball – because the TD wasn’t involved in awarding the comp ball. This is similar to the player concession rule – it’s only valid and official if the concession is communicated to a TD.
Given the context, I also agree that Andreas’ solution is quite compassionate and not inappropriate. But… it creates an undesirable slippery slope of inconsistency, where all your rulings as a TD based on IFPAPA ruleset get now be questioned by players asking for leniency/loopholes.
Ramifications of going by the rules: 1 pissed off player, and 4 (or more) players realizing that the rules are the rules, and officiated by the TD (not them).
Ramifications of granting leniency: unlimited # of players that will be pissed off because you don’t grant them leniency on their future misstep, or pissed off players that you are bending the rules.