Did the man lock up his 6-year old son at home overnight? (把6岁大的儿子一个人锁在家里整整一夜)
Your understanding of the sentence is correct. The man in the story did lock his six years old son alone at home for entire night so that he could help a woman. 

The writing of that woman illustrated she is a self centered person. And the man was a horrible father.

Side note:


  Around 1997, I watched in the news in Hong Kong that there were two working parents who kept their two preschool age children locked in at home during their working hours, because they couldn't afford daycare. Unfortunately, a fire broke out in that apartment and the two kids couldn't escape  because the door was locked and were killed in the fire. The parents felt so guilty, they hanged themselves within few days.


That's why I feel so strongly about locking kids at home by themselves-- Nothing worth the risk!