Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.
Wa alaikum assalam wa rahmatullahi wa barakatuh.
As to what follows:
With regards to answering your question we say, success is by Allah Almighty.
The talk is not correct, maybe the imam assumed that from the saying of Allah’s Messenger (peace be on him) in a hadith narrated by Muslim (869) which was reported by Amar (may Allah be pleased with him) who said that:
I heard Messenger of Allah (peace be on him) saying: “Prolonging Swalah (prayer) and shortening the Khutba (religious talk) indicate the religious knowledge of the person. Make your Swalah long and your sermon short.”
However there in this hadith there is no indication on giving a talk before Khutba, but the indication that is there is shortening the Khutbah and Prolonging Swalah. The type shortening that is permissible is that which does not disrupt the objective of the khutbah which is reminding people.
As for the lesson before Khutbah, I fear that it may be regarded as a third Kutbah. Neither the Prophet (peace be on him) nor his sahabah did that. It can also be feared that it might fall under prohibited halqahs (gatherings in circles) which are done before swalah. The prohibition on these halaqahs is mentioned in a hadith narrated by Abu Dawud (1079) and Nasaai (704) which was reported by Amr Ibn Shuaib from his father, from his grandfather that:
“The Prophet (peace be on him) forbade sitting in circles on Friday before Jumu'ah prayer.”
Some scholars have said that the reason for this prohibition is that Knowledge and study gatherings disturb prayers and their preparation.
My advice to you is that you should carefully advise him and clarify what is correct to him.
And Allah knows best.
Your brother,
Dr. Khalid al-Muslih
20 / 9 / 1427 AH