Why did Muhammad say, "May your mother be bereaved of you"?

In Sunan Ibn Majah - 4048 , it reads: > "The Prophet (ﷺ) mentioned something and said: ‘That will be at the time when knowledge (of Qur’an) disappears.’ I said: ‘O Messenger of Allah, how will knowledge disappear when we read the Qur’an and teach it to our children, until the Day of Resurrection?’ He said: ‘**May your mother be bereft of you, Ziyad**! I thought that you were the wisest man in Al- Madinah. Is it not the case that these Jews and Christians read the Tawrah and the Injil, but they do not act upon anything of what is in them?’" Would not wishing grief upon someone's mother be very extreme? In another hadith describing the same situation (Jami` at-Tirmidhi 2653 ), it reads: > "Narrated Jubair bin Nufair: from Abu Ad-Darda who said: "We were with the Prophet (ﷺ) when he raised his sight to the sky, then he said: 'This is the time when knowledge is to be taken from the people, until what remains of it shall not amount to anything." So Ziyad bin Labid Al-Ansari said: 'How will it be taken from us while we recite the Qur'an. By Allah we recite it, and our women and children recite it?' He (ﷺ) said: '**May you be bereaved of your mother O Ziyad**! I used to consider you among the Fuqaha of the people of Al-Madinah. The Tawrah and Injil are with the Jews and Christians, but what do they avail of them?'" Jubair said: "So I met 'Ubadah bin As-Samit and said to him: 'Have you not heard what your brother Abu Ad-Darda said?' Then I informed him of what Abu Ad-Darda said. He said: 'Abu Ad-Darda spoke the truth. If you wish, we shall narrated to you about the first knowledge to be removed from the people: It is Khushu', soon you will enter the congregational Masjid, but not see any man in it with Khushu'.'" In this hadith the wording is a little different, so Muhammad wishes death upon Ziyad's mother this time. So my question is wouldn't it be immoral for Muhammad to say these things?