In the old testament the Holy Spirit was not indwelling and His presence was not guaranteed always. There was temporary inspiration that came upon different men to carry out great and mighty feats for God.
In the Old testament the Holy Spirit inspired all kinds of men.
Great men and prophets such as Daniel, Ezekiel, Othniel, Joshua, Gideon etc just to name a few,produced outstanding results through the sometimes overwhelming inspiration of the Holy spirit.
Prophets were able to write scriptures in such a way that there was unity in them . Even if some of the Prophets never knew or met themselves, this was able to be achieved through the inspiration of the Holy Spirit. This inspiration is what false prophets never had.
The inspiration was not forced or triggered by them but the Prophets could put themselves in a place where they could recieve from God .