and were not just whistling dixie

And were not just whistling Dixie is a cliche idiom term referring to talking in fact and being serious about something that seems far-fetched. Whistling Dixie is a slang term which means unrealistic fantasizing, so when someone says they arent just whistling Dixie, they are saying that even though it seems far-fetched, they are actually being truthful and serious. It is commonly used after a person tells a story that doesnt seem realistic but in order to prove it is truthful, will say they arent whistling Dixie.