Sounds legitimate. Don't bother with immigration lawyers. The DV program does not allow appeals but your best bet would be to email the embassy asking for an appointment to see the consul general and explain your case. The CO should have put you on consular processing to seek guidance on the issue before making a decision to deny you. So, if you were denied outright without CP, you may have a chance. However, if you had already been placed in CP and then later denied, don't waste your time. Just enter the lottery again this year.
Wish you all the best.