He writes that "0.005 USD" is just an arbitrary value.
That would be oversimplifying my words. Try: "I have learned of several isolated trades during the time period, none of which has happened at below 0.001 or above 0.01. Because the trading was non-continuous and the individual circumstances may have affected the prices, volume data is not available to me, and many other factors, I have approximated 0.005 for the whole period with no trend."