Lots of companies use Microsoft's "Azure" cloud storage and content delivery services, including Apple at one time. I believe Apple has since moved everything in-house, but nothing is stopping them from using Microsoft or a similar service such as Amazon's AWS. It's all about cost, and their services are cheap.
Personally I wouldn't worry about it, but I appreciate your desire to know who and what is storing things on your Mac.
You can almost certainly delete that cache file but it is just as certain to appear again. Determining the culprit amounts to satisfying one's own curiosity, and there's nothing wrong with that.