Working engineer here. A lot of social ineptitude throughout the industry, at least with respect to interaction with non engineers. Certainly can't help the arrogance thing.

However I think assumed confidence outside of one's field is a result of what an engineer should be. Engineers solve problems with incomplete information regularly. So when approaching a field he knows little about, an engineer will not hesitate to be as confident as he is in his normal field. Business as usual. I don't think it would be hard for that to come across as arrogant.