Storms are usually over by 8 or so in the summer. I really don’t find it difficult to keep horses in, in front of fans, during the heat of the day, and put them out around dark. My horses have only ever stayed in over night like 2 or 3 times a summer. And I like my sleep. I’m not going out at 10 or 11 to bring horses in or put horses out, unless it’s an emergency.
As far as the alarm at the track, I suppose it’s possible, but it’s far more common for tracks to have loose horse alarms. Maybe someone mistook a loose horse siren for something else?