Bayer won the match 2-1 on October 18 thanks to a Kiessling header that went through a hole in the side-netting after going wide of the post.
Referee Felix Brych, who awarded the goal, told a hearing: "I thought that the ball was going wide. I lost it because my line of sight was obscured, And then I saw, the ball was in the goal."
Kiessling, who has been criticised for celebrating, added: "I saw the ball fly in the direction of the side-netting. My view was blocked and I did not see the impact, but the ball was in the goal.
"My first thought was that the goalkeeper had turned it in himself. I thought of everything, but not really of a hole in the net."
Hoffenheim now have a week to decide whether to appeal further.