Funny, I have a different interpretation to "the incident with the dragon", that Gandalf is intentionally underplaying the consequence of his "little nudge out of the door".

Sure the original intent of the quest was mostly one of curiosity and greed, but it resulted in the Battle of the Five Armies. Which of course is much less of a huge deal in the book as it was in the movies (The Battle of Five Paragraphs more like), but still has significant implications for those involved.

Gandalf saying he was "barely involved" is also being quite generous to Gandalf's involvement, as he a. picked Bilbo himself, b. provided the map and key needed for the quest's completion, and c. served as a primary guide for the majority of the quest.