I was looking at the arrow construction that pierced the ML heart, and it doesn't. appear to be the one that the FL released. Are my eyes deceiving me? 

Yes. FL shot the ML

Fl shot him, in one of the ep it said that she could have shot him deeper but she shot him in a way that is fatal but also no so fatal, so in a way she saved him.

If you watch the fl closely , you will see that she drew two arrows. First arrow she shot, ml dodged it but the second one which came immediately after the first one wasn't easy to dodge