Why is this tenses sheft?

[Latoof]

I read this sentence in a novel I am reading and I want to know why the sheft in tenses from past, which the novel is pased on, to the present tense?

The sentence is as follow:
But the Ibo people have a proverb that when a man says yes his chi says yes also.
This sentence did not appeare in the middle of a dialouge, which must be written in the present tense as characters should say it in the present.

[Latoof]

The same appeared again in the following sentence:
In the end he decided that Nnadi must live in that land of Ikemefuna's favourite story where the ant holds his court in the splendour and the sands dance forever.
Is it because it is a story telling , which must be told in the present tense?

[Tdol]

In the examples, the present suggests taht they are still true- the ant stills holds his court. We don't have to use the present in story telling- we can if things are still true or to make it more alive.