Ehrman's point in that blog post is not whether the New Testament is considered historical literature, but whether the expertise gained by scholars who work on the New Testament is as historians or as something more literary-critical.

It is in this sense that he writes: "There are a number of Hebrew Bible scholars, for example, who are particularly trained in and expert on the history of ancient Israel. In order to determine what happened, historically (say in the eighth century BCE, or the sixth century BCE, etc.). These scholars utilize the biblical texts and all other relevant information – including archaeology, texts from surrounding civilizations (Egypt, Babylon, and so forth)."

I can make an analogy to my own field, ancient philosophy scholarship. I wrote my dissertation on Plato's dialogues. Plato's dialogues were written in the first half of the 4th century BC, and they are set in between the second half of the 5th century BC to 399 BC.

We can study Plato's dialogues two ways. We can study them as historical documents that tell us about the Athenian intellectual-cultural-political milieu at the time, and learn historical facts about how a segment of the population responded to goings-on, such as the end of the Peloponnesian War, changing attitudes towards Sparta, and so on. But we can also ask questions like 'how does the argument in this passage go?' or 'what is the meaning of this simile?' and things like that.

Ehrman's point is that we can use the Bible to do those same things. Some people study the Bible in order to learn about historical facts, such as how a community thought of itself and how it was responding to various events, and other people can study the Bible for the sake of interpreting it as a text.

The fact that it can be used to learn about historical facts answers your question "Is the New Testament considered 'historical literature'?" with a "yes". But not everyone treats it that way when they are being trained as a scholar.