A "reunion" need not be a "meeting". For example, a "family reunion" in which members of a family travel to one location to see each other and to enjoy each other's company, is like a dinner or a party, but it would not be anything like a business meeting.
A reunion also requires that the people have a prior connection -- for you cannot reunite something that was never united before. It is very common, on the other hand, for "meetings" to involve people who have never seen each other before, and who are complete strangers to each other.
"Meeting" in English means exactly the same thing as cognates of "reunion" in several Romance languages, including French and Spanish, and perhaps others I don't speak, as well as Italian. "Reunion" is a false friend. You will have to forget its meaning in your native language while you are speaking English.