Another Blatant Nasibi

I got someone to translate this for me and he   wishes that he was the killer of Imam Husayn, to "realize the reward of following the Sunnah.

This understanding is taken IMAM IBN ABDEL BARR and sadly he is a Maliki.

Now the defense for this is he supposedly  is referring to a Hadith in Al Bukhari (or Muslim) where the Prophet (peace be upon him) ordered to kill the one who claims to be the Khalifah if there is already a Khalifah.

On the contrary, Yazid was King. He was not a calipah. The Prophet (pbuh) said the Caliphate will last 30 years. Therefore, how can this rule extend to Muawiyah and Yazid ?