Based on the grammar and language of the poster why is it surprising that Tubman is referred to illiterate

Incomplete question. However, I assumed you are referring to this poster.

Explanation:

Interestingly, we notice that Harriet Tubman made use of figurative language in her words. She used the literary device of personification; in which a thing or condition is spoken as though it was human or living.

By this using such kind of expression that has been used by literate individuals,  it makes it surprising that Tubman is referred to as an illiterate.

For example, she personified "death", and "liberty" as objects she could have, obviously those were beautiful words which we expect only an educative person to say.

lol for the pointsss