Guest complained about noise from neighbouring room — already checked out, now leaving a bad review

Difficult situation: a guest in room 14 was disturbed by noise from room 15 during their 3-night stay. They mentioned it at checkout and I apologised, explained room 15 had a large family, and offered a 20% discount on their next stay. They seemed okay. Then two days later, a 2-star review appeared. I feel like we handled it reasonably — the noise wasn't from our staff, just other guests. How would you respond to this publicly? And is a discount on a future stay the right kind of compensation?