It doesn't explicitly say this but the passage strongly implies that the coins are more likely to have come from a pilgrim than from a trader. We are told that there are two options, and that the coins are uniform. We are then told that if the coins belonged to a merchant, the coins would likely have been more diverse.
From this we can infer that it's unlikely that they belonged to a merchant, and thus, it is likely they belonged to a pilgrim.
