Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.
As to what follows:
In response to your question, we say, and with Allah Almighty lies all success:
Ilhad is linguistically taken from lahd, which means inclination or deviation. It has become predominantly used for describing deviation from the truth to falsehood. So the meaning of the Shaykh’s statement in describing the innovation of the Khawarij, that it wasn’t out of ilhad, i.e. it wasn’t with the intent of deviating from the truth and guidance, rather it was out of seeking the truth and guidance, but they went astray from the path and were not successful in arriving at the truth, as has been narrated from `Ali bin Abi Talib (may Allah be pleased with him) when he was asked about the Khawarij; are they disbelievers? He said, “It was from disbelief that they fled,” i.e. that they never took on those views except trying to flee from disbelief and seeking the truth, but they did not arrive at it.
The most well-known thing that the Khawarij became known for was their extremism in takfir (accusing a Muslim of being a disbeliever) and giving preference to the texts mentioning Allah’s threat of punishment over the texts mentioning Allah’s promise of forgiveness and reward. The scholars, past and present, have spoken about their innovations and clarified their misguidance.
As for the Shaykh’s statement concerning the Rafidah, that the origin of their innovation was based on ilhad, then it is because deviation from the truth and following desires is excessive among them.
As for their innovations, then the scholars have mentioned them in detail, refuting their misconceptions, the most dangerous of which is shirk with Allah Almighty, believing in the infallibility of the twelve Imams, cursing the vast majority of the Sahabah by accusing them of being disbelievers and defiantly disobedient, and saying that the Qur’an is distorted.