I am sorry for what happen.
And it is not your fault.
I agree that we should train our dog to obey "Stop" or "Stay" command in case of run away situation.
I also agree with your friends (co-worker) not to contact the owner.
With what you describe the situation, he is not concern of the dog's welfare and I suspect he will take an advantage of you and the situation to get money from you.
But I pray for the dog that he/she is O.K.
