Midfielder Dembele was sent off for a gentle shove on Wisla Krakow's RADA-trained Argy midfielder Gervasio Nunez.
And he said: "I didn't have a very happy experience in Europe last year but it will be better with Tottenham. We have the confidence to go a lot further. It was not easy to take the red card.
"The guy stood on my foot and when I turned round and pushed him very softly on the shoulder, he fell down dramatically and I was sent off. I have to learn from this.
"I don't agree with people who dive to get opponents sent off. It's a bigger problem in Europe than in England."