How does Jim's manner of escape demonstrate his intelligence?

Do you mean his escape to the island..... and the fact that he just hid out?

Jim swears him to secrecy before revealing that he has run away from Miss Watson. Huck is immediately faced with the responsibility of protecting Jim or telling the town the truth. He chooses to stay with Jim because, as a young boy who has lived outside of main stream society for quite some time, he still lacks the prejudices of the older folks in his town.