Assalamualaikum sheikh.I saw a video of famous dai(Ahmed deedat)who share a story of christian man and sheikh debating.The sheikh made a point that Allah cry(naudzubillah)because he cant save his own son to the chrostian missionary.Ahmed deedat(May Allah have mercy on him) tell this story at his lecture and people start laughing.Is this kufr or not.

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.

The utterance of that statement was mainly meant to deny the Christians’ creed of Crucifixion! As such, laughing at such a situation can be understood in light of disapproval and denial, not approval and acceptance! So, this cannot be considered some kind of disbelief, rather it is something that is allowed. Imam Muslim narrated that the companions used to enter into conversation with one another and would talk about things during the Days of Ignorance, and they would laugh while Allah's Messenger would smile only.

In his Ikmaal Al-Muʿallim, Qaadhi ʿIyaad said, “This report indicates the permissibility of talking about the news of the pre-Islamic period of ignorance and other nations. It also indicates the permissibility of laughing.”

In his Mirqaat Al-Mafaateeh, Al-Qaari said, “The statement (and they talked of the things that they did during the Days of Ignorance) means that they used to speak in dispraise about them or to narrate their stories to allow others get the benefit of them. For example, one of them once said, 'Your idols never benefited you as much as mine did.' So, they asked him, 'How?!' He replied, 'I made it of Hais; so, when the drought afflicted us, I ate part of it every day.”

Allah knows best.