Is what transpired between the father and his friend, involving joking and saying "I agree," considered a valid marriage contract for their son, and how can it be undone if that is the case?

What transpired between the questioner and his friend is not considered a valid Islamic marriage contract (nikah) due to the absence of its essential pillars, such as the pronouncement (sighah) indicating the contract and the presence of witnesses. The father of the girl's statements, "When will he marry her?" and "my daughter," are not considered a valid legal pronouncement for marriage. It is advised to avoid jesting in matters of marriage, as seriousness and jest are treated equally in this regard.