Dear friend and My dear Bro I want to say something that Muslim is one who believes in one God Allah, and Muhammad (Peace be upon him) as a messenger of Allah and the holly book Quran. If you want to know about who is Muslim don’t look at Muslims as they are now Read the Quran and read about the life of Prophet Muhammad (Peace be upon him).
You are Right a person may do Good which he may think is good by doing so he will not become a Muslim he only become a Muslim by responding to the instructions provided By Allah Almighty which he has sent for the guidance called Quran.
Many people think that Muslims are terrorists but it’s not true Because Islam teaches us that not kill old persons, children, women, and not kill those who want peace IN WAR. So think that how a true Muslim become a terrorist? Islam is the religion of Peace each word of Quran teaches us Humanity, Love, and Peace, if you have misconceptions please Read Holly Quran…
I hope this will be the answer of your question thanks.