Forkdelta is a decentralised exchange and anybody can set any price they feel comfortable with, if it's a great if token, you will see very good prices for large quantities but if it's a shitcoin without liquidity, you are likely to see the kind of discrepancy that you mentioned.
that is, the seller is free to put any price on the token he/she will sell. Buyers can put prices as low as possible. Usually less valuable tokens are traded there lately. That is the fact, the gap is too high. Forkdelta performance is like that, the API is low.