Is it a mistake to instruct a disbeliever who wishes to embrace Islam to recite the Shahada, and is this statement considered an act of disbelief (kufr)?

The questioner and her husband erred in judging their friend to be a disbeliever (kafir), due to the possibility of impediments to declaring someone a disbeliever, such as ignorance or misinterpretation. Furthermore, their friend's statement is not originally an act of disbelief, but rather a sin. The application of the ruling of disbelief to specific individuals is the prerogative of deeply knowledgeable scholars. Disbelief does not revert to the questioner and her husband for their statement, because they said what they said out of misinterpretation or ignorance.