It sounds as though the car alarm issue is normally fine in her listing! Seems like the guy was just trying to get a free stay/refund he wasn’t entitled to because he could stay at a friend’s house. We should object to that on principle.
Luckily I have never had problems with someone’s car alarm, but if I did it would be thumbs down. I don’t expect to have to put anything about car alarms in my listing, it should be covered by common sense and existing quiet time rules. My neighbours have work, school and businesses to take care of, no space in our lives to be woken up by car alarms or any other guest noise problems. No wonder Airbnb is banned in some districts if guests cause problems.