A non believer is not going to be considered by God as a man after his own heart. In fact, Many believers will not get this honor.. Very few people will get this, I am not even sure I have this honor. In fact I would say I do not..
I have seen men go to the altar and say they got saved every single service..... they were seeking, like David, David desired to please God's heart persay. that's not salvation...thats a strong desire.....don't we all long to find favor with God.... we Christians desire to live the way his commandments instruct us to. being a man after God's heart is pleasing to God, he sees a person that wants to please him.... its still not salvation