When we talk about the Arabian Sea trading network, it usually is implied to mean the time from which the Europeans started sailing through the region. But as Manmadhan Ullatil pointed out in Hubs of the medieval trade, this trading network existed much before this period. In fact the ports along the coast of India and Africa were part of the trading network of the Old World. By studying the Prehistoric movement of plants and animals, we are able to reconstruct the trading patterns and speculate about the traders.
In such a study, something interesting has turned up. Researchers looking into the domestication of banana found that it may have been initially done in New Guinea; wild bananas are found in South Asian rainforests. By looking at the banana phytoliths, it is now believed that bananas reached the Harappan region around 2000 BCE, before the decline of the civilization started and apparently were not used for eating. So what else could they have been used for?

Given the distribution of wild Musaceae in South Asia, and the climate at that time (Asouti & Fuller 2008, Madella & Fuller 2006), it is unlikely that these could derive from the ancient presence of wild Musa or Ensete. The possibility that a species was cultivated as a garden ornamental or as a source of fiber and raw materials (e.g., for paper) cannot be ruled out. Indeed, one of these nonculinary uses of Musa/Ensete might be a more plausible explanation for these phytoliths than an early dispersal of edible cultivated bananas from Island Southeast Asia by the third millennium B.C.[Banana Cultivation in South Asia and East Asia: A review of the evidence from archaeology and linguistics( via Carlos Aromayo)]

The paper says that it is possible that the Indus people used the fiber for making paper. Now if they made paper you would think that the next step would be to assume writing. But claiming that Indus people were literate would violate a lakshmana rekha.
So the next line in this paper says that since few folks think that Indus people were illiterate, this could not have happened. Thus apparently, Indus people got bananas, did not eat them, made paper and threw them away. They could have done anything, except writing on it.