All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
With regard to your first question, if that misconception is so widespread that it needs an answer and clarification from the Mufti, and the Mufti was able to remove it and there is a benefit in raising it in this forum, then there is nothing wrong with that.
However, if it is a misconception that is not widespread and raising such a misconception would lead those who are following this forum to confusion and doubt, then it is better to avoid raising it. If a person finds any doubt in himself, then let him look for an answer to such misconception privately without raising it in public forums or means.
As for your second question, it seems that it stems from whispers (Waswasah), as issuing a ruling on a person that he is a non-Muslim (disbeliever) is not an easy matter; rather, some conditions must be met while there should not be any Islamic impediments for declaring him as such.
It is believed that this father who prays is not a disbeliever even if he has some misconceptions or errors in some matters. Therefore, you must avoid these whispers and not be hasty in judging any specific person to be a disbeliever or an apostate without the eligibility to issue these judgments.
Allah knows best.