He is stating that all Christians are “one”.
He’s talking about Satan’s perspective in trying to eradicate Christianity. In fact, many of the Christians who’ve been killed in Iraq and Syria are non-Catholic Christians. You think Satan isn’t being their persecution?
Well, he's right about this. Obvious NT teaching.
The term "Christian" has several different definitions. At the heart of things, being "Christian" is not the same as being a member of a particular religious organization. They may be related overlapping categories, but not interchangeable. There are Catholics who are not Christians and there are Baptists who are not Christians.