First thing, they aren't the same or interchangeable. Cajun music and zydeco are also not the same. Cajun and Creole cooking aren't the same either.
Let me break it down for ya, cher:
Descendants of the Acadians expelled from Nova Scotia. They brought their own culture and cooking.
Descendants of French and Spanish people who settled in Louisiana during the time the Louisiana territory was in possession of those two countries. Whites used this term, and so did the offspring of wealthy French or Spanish men with Black women. Which is why whites stopped referring to themselves as "Creole" at some point in the late 19th Century. Though that's been changing for a good decade or more.
Louisiana Creoles, French speaking people of color,
created this distinctive blend of music that fuses blues and R&B with what's called swamp pop or Cajun music.
A blend of Acadian music, blue grass, and country music using instruments such as the accordion, washboard and guitar mainly.
Last note: Louisiana Creole French is almost extinct, victim of the aggressive and sometimes brutal efforts to make French speaking Cajuns and Creoles more "American". Creole French is very similar to Cajun French, but not the same. Some of the terms and phrases are different, influenced by African languages and Native American terms. Also influenced by early immigrants from the Caribbean, Saint Dominque (modern day Haiti), Trinidad, the Dominican Republic, etc.
Okay, that's a short version. Trust me, it's way more intricate than what I just outlined! Yes, we're all mixed up like a big pot of gumbo (invented by African-American slaves by the way, not the Cajuns).