@Olivier5,
The text exists to the tribesman, but not as text: the ink and paper might as well be a Rorschach test. Maybe he's thinks they're insect droppings. Certainly not information. There is no intrinsic information there.
If I created a hoax "book" full of fake symbols arranged in fake frequency distributions and fake syntactical arrangements, someone might assume it was text they couldn't read, because it has all the trappings of text. But it isn't text, it's gibberish.
Text is something that consists -- to a particular viewer -- as.meaningful communication through linguistic or other (e.g. mathematical) symbols. But even then I could argue about it. I've seen patterns in naturally occurring things like rocks, that looked an awful lot like text, sometimes even real English words. Heck, just take a bunch of coffee grounds and push them gently around with the tip of a knife, and it won't be long before strings of letters and numbers emerge. Unless you assume that God, or the spirit world, or some removed aspect of your own mind is trying to send you messages, it isn't really text despite the coincidental appearance of text.
Even text designed as text has as many potential meanings as there are possible systems of interpretation. I could come up with a cipher system and a key that, if applied to this comment, deciphers a completely different message. Is this plaintext or ciphertext? That's how cranks find secret messages in Shakespeare proving he's really Bacon.
How about text that's printed in a foreground background combination that's invisible to the color blind? I could fill a hundred pages with cuss words, call it a blank journal, and give it as a gift. It's text to me but not to him.