The fact that Ingold asks "what" Pippin is just seems to reflect the uncertainty of the situation, what with war going on, and not being able to trust anyone. Also, it seems to me that people love to categorize other people, and if they can't then they get uneasy. When asked about my heritage or religion, people often ask, "What are you?" I'm tempted to reply, "Well, I'm human, female..."
On a certain level, though, I can understand his reaction, which is near disdainful. Pippin doesn't look like much of a fighter, and Ingold has no way of knowing all that he's been through. He might view Pippin as just being in the way if he can't help fight.