Danzo does not have just 1 chakra nature, he has Wind, Earth, Water, and Fire Release, as well as Yin and Yang Release. just like Sasuke who has a few natures he c*e but is counted as Lightning even though most Uchiha's are fire. they are In the Land of Fire so it makes sense most clans that originate from there are fire.

Torune is a bug/poison user and they are classified as Earth for whatever reason, maybe cause shino actually does earth nin-jutsu or earth and bugs go together. Either way he is by no means a Fire or Lightning, most non nin-jutsu ninjas are listed as earth such as Lee.

Also remember we only really seen Danzo fight once which he was using Wind against someone using Lightning, it is possible he was using it to counter the lightning. this last thing is just a guess with no actually proof to support it but the previous 2 are both easy for you to google and see for yourself.