We had a better team than Tunisia & deserved to win so you cannot rule out BAD LUCK.
1. Tunisia was supposed to beat Gambia in their last game to avoid Nigeria vs Tunisia in R/16, but received red card & eventually lost the match.
2. Their Covid-19 cases actually put us at a psychological disadvantage because many then expected us to win easily thereby putting undue pressure on us.
3. When you play under pressure, you are liable to mistakes which is the root of Iwobi's unlucky red card.
4. Buhari factor.