Arjuna asks a question and addresses Krsna as bhavata and twam. Bhavata is a respectful address while one saystwam to a friend. It is like saying aap and tum in Hindi while speaking to the same person! Arjuna acknowledges that Krsna is his guru as well as friend.
Arjuna views Krsna as a limited individual like any other person and is oblivious to the fact that He is an avatar, realized at birth! He has transcended the body, mind and intellect and become one with Atman. So when He says ‘I’ He means Atman and not the physical-emotional-intellectual personality.
In fact whenever there is any spiritual interaction it is Atman that communicates. You can teach only to the extent you have unfolded Atman and lived the principles you are teaching. The rest falls flat.
Hence Swami Rama Tirtha advises us to separate the teachings from the teacher. Follow the teachings. You can never go wrong. If the teacher is a realized Soul you cannot understand that State so you will err in your judgement. If he is wrong you get misled.