He divorced his wife three times in a state of extreme anger
For divorce to count as such, it is not stipulated that there should be witnesses to it; rather divorce (talaaq) may occur without any witnesses.
When divorce is issued in anger, in some cases it counts as such and in some cases it does not. The anger in which divorce does not count as such is extreme anger in which a person does not think straight and utters the word of divorce without meaning or wanting to. For a detailed discussion on that, please see the answer to question no. 45174
The threefold divorce counts as one talaaq, according to the correct view.
See the answer to question no. 170606 and other questions referred to therein.
If a man clearly utters the word of divorce (talaaq), then it counts as such, whether he intended it or not, because there is no stipulation that the intention be present in the case of a clear statement, unless he was forced to issue the divorce or he was in a state of extreme anger, in which case his divorce does not count as such.
See also the answer to question no. 174341.
If you have consulted a scholar whom you trust, you should accept his opinion and not look for another view.
And Allaah knows best.