In the name of Allah, the most gracious and most merciful. May Allah's perfect blessings, prayers and peace, be upon the most noble of creation. The best of messengers and the leader of all man kind and Prophets. Our beloved master and intercessor, Sayiduna Mohammed (peace be upon him).
The man is told to accept Islam and go against his nafs (the inner ego and caprice). If you look at the islamic tradition and the blessed Sunna, we are taught constantly to fight our inner self and inner ego. For example when we dislike the fact we have to wake up before dawn to pray fajr, we still do so because we know it is better for us. Similarly this man dislikes the idea of becoming a muslim, and the prophet, in all his wisdom is telling to accept it because he knows it is better for him.
There was no compulsion or force in him accepting the religion, just that the prophet (peace be upon him) telling him to accept it (and fight against the influence of satan and his ego).
I hope that clears it up for you. May Allah guide us all to the correct islamic understanding, and increase our love and obedience to prophet Mohammed (peace be upon him) and his blessed family and noble companions.