Not exactly - they Can do that, but they don't need to match - using cloudfront in front of your s3 website and then the site can be served from any bucket or folder within a bucket.

I have dozens of s3 static websites served from a single s3 bucket, all with unique top-level domains, each in its own folder within that single bucket - much easier this way.

Given anyone can create a bucket with any name (if its not already in use), you can't count on getting the bucket name that matches your domain name.