Firstly, this sentence should read "He came across as being rather arrogant during the interview" (no "than").
As for your question, "come across as" means "appear to be." In other words, based on the body language and the way someone is speaking, the impression they make on you is what they "come across as." In your sentence, the person who was interviewing for the job seemed very arrogant to the person conducting the interview (it could be the way he talked, it could be the way he sat, etc.).