Upon reading your post, the first thing that confuses me is that you state you are accessing 2.0 and your code shows 2.0, but the response back says the URL is 1.1.
Another thing that confuses me is that the response is 200 (OK), and it's trying to hand you a binary (file).
Now, I am not at all familiar with smartsheet, have zero clue what that is. But it appears that the response is good and it's sending back either a file, or some kind of struct that contains a file.
Have you read and understood the smartsheet API documentation? Does it state specifically what the API is sending back on successful connections?
I got it working by setting the CFHTTP attribute getasbinary="never".
also converting the returned fileContent object into a string using:
<cfset rawJSONString = httpResp.fileContent.toString()>
worked for me too.
Thanks for you help
@Bygra, please mark your answer as correct. It will help someone with a similar problem.