Bruno never said Rudel was not a Nazi.
All he did was just confirm a few facts about Rudel - he's wasn't "officially/technically" a member of the NAZI party.
Ofcourse, the cute part of Bruno is that he just takes things too seriously

In this case, he should have considered our usage of the term "Nazi" not as someone literally holding an official membership of the NSDAP, but rather a more generic term for German military/civilian officials who heavily sympathized and supported the NSDAP politics and way of thinking.
