Why the Roma (& some other Gypsy-like people) are called the Bohemians?

The word Bohemian used as an exonym for the Roma in France and other French-speaking countries, same as in some cases in Spain is because the Roma came there in 15th Century from Bohemia which is a part of the nowadays Czech Republic.

It was because those Roma said that they are Bohèmiens = Czechs.