Don't know...
here in the city, I often hear the siren being turned on and off while they drive through the city. Maybe on a clear road they rather have turned the siren off... Maybe turned out not being necessary at all, when they got a closer look in the ambulance and it seems not being critical.
One can only hope..
Fact is, you did a very good think to help the poor guy. Not everyone knows how to deal with such situations. And hardly anyone knows how to deal with such situations correctly.
And now you make a nice cuppa tea for yourself and so, call your sis to have a bit chitchat, and overall make yourself comfortable, it has been quite shock for you I guess.