Does triple talaq take effect because the husband made his wife swear to believe his mother about leaving the room, and then the husband remembered that this had happened before?

The majority of scholars hold that swearing by divorce—whether intended as an actual divorce, a threat, a means of prevention, an instigation, or an affirmation—results in divorce upon breaking the oath. They also believe that uttering "triple divorce" constitutes three divorces. However, Sheikh al-Islam Ibn Taymiyyah is of the view that swearing by divorce, when the intention is not to effect a divorce but rather to threaten or affirm, is akin to swearing by Allah. In such a case, the swearer must pay an expiation for breaking an oath (kaffarat yamin), and no divorce occurs. When divorce is intended, he believes that uttering "triple divorce" counts as a single divorce.

However, since you swore by divorce believing yourself to be truthful and did not intentionally lie, the preponderant opinion is that no divorce occurs, as stated in the fatwas of Sheikh Ibn Baz. It is important to avoid swearing by divorce, as it is prohibited. Lawful swearing is done by Allah, for the Prophet, peace and blessings be upon him, said: "Whoever swears an oath should swear by Allah or remain silent."