Was abandoning the prayer behind an imam who sought the help of the Prophet (PBUH) – and justified it by saying that it was out of veneration for the Prophet, not out of belief in his divinity – actually correct, and is his statement considered disbelief?

Seeking aid from other than Allah Almighty in matters that none but Allah can control is disbelief that expels one from the fold of Islam. There is no harm in refraining from praying behind an imam who seeks aid from other than Allah, in pursuit of perfect prayer and avoidance of doubts. Nevertheless, it is not permissible to declare this imam or other Muslims who seek aid from the Prophet, peace and blessings of Allah be upon him, as disbelievers, except after establishing the proof. A Muslim may commit major disbelief without being declared a disbeliever due to the presence of a barrier, such as misinterpretation (ta'wil), coercion, or ignorance. There is a difference between judging an act to be disbelief and judging its doer to be a disbeliever.