I never liked John MacArthur's teaching, no matter what it was on. His radio program, falsely called 'grace to you' was not grace at all. It was nothing but grace plus works. Plus, in the tenor of MacArthur's voice was always a 'holier than thou' presentation. A condescending tone which I hated. He is a legalist, though he would deny it.
So, I am not surprised that he wants to brand a certain part of Christianity as 'strange fire'. As a legalist he must be the only one that represents the true church. God can't work through others. He must only work through what MacArthur believes.
Stranger