Elric was observing and listening to their short conversation from the distance with his focused ultra-sensitive ears and learned something about the young man they were following.
It turns out he was a Dragon that had transformed into his human form who seems to have given up his Dragon essence. Which explains why Elric could never connect who he was according to his memories. He was a Dragon all along!
Moreover, it seems that this young man holds a clue about what happened that night. So Elric decided to keep a tight watch and step out once they make a move to kill the young man.
However, the Dragon hunters finally showed themselves and revealed their intention to force the young man to redeem is Dragon essence back - only to become their take-home of course.
The young man fought back in retaliation and ended up hurting himself.
