It means that the coin has lost approximately half of its initial value. Polybius was 10 times cheaper on the exchanges after the ICO. Most probably you are going to see this in the majority of new ICOs because of the falling BTC.
I also have the same question as the OP, does it mean the rest of the coins are kept by the Exchange?
Does market cap means total value of the coin? Not the amount of coin itself? Because all this time I thought market cap is the total coin at the market.
Market cap is a simple function of TotalShares(in this case total coins) x Value. So If a token has 100,000,000 units and each unit is worth $1 then it has a market cap of $100,000,000. If the value goes down to $0.01 then it has a market cap of $1,000,000. The number of coins don't change.