You are a simpleton, Hegesias;

[GoldfishLord]

Like Socrates, Diogenes favoured the spoken over the written word. When a man called Hegesias asked to be lent one of his writing tablets, he replied, "You are a simpleton, Hegesias; you do not choose painted figs, but real ones; and yet you pass over the true training and would apply yourself to written rules."

Source: Psychology Today | Are You a Cynic? Really?

I'm not sure what they are saying in the bold part.
Would you explain the bold part?

 

[Tarheel]

See it as an expansion or explanation or example of "Diogenes favored the spoken over the written word".

 

[GoldfishLord]

What does "his writing tablets" refer to?
What's the meaning of "tablets"?

 

[Tarheel]

Nowadays we use paper to write on. They didn't have paper then. They used clay tablets.

 

[GoldfishLord]

Would you elaborate on "you do not choose painted figs, but real ones; and yet you pass over the true training and would apply yourself to written rules"?

 

[Tarheel]

Diogenes favored speech (true figs) over writing (painted ones).

Somebody saw a reason to write that or we wouldn't know that, would we?