Hi,
I've checked several sources for you (e.g. here and here), just to be sure of what I posted earlier today (I was in a hurry so I wasn't able to double check).
The account is normally created under Windows as part of the .NET-developperframework. Normally it is hidden under Windows. But because you've migrated from Windows to Mac, automatically the hidden 'user' has also been transfered. Because your Mac doesn't hide stuff from you, it shows as a normal user.
It enables you, as developper, to run Windows-services on your server. Being a fact that you cannot run Microsoft's .NET on a Mac, feel free to delete that account. 😉
In reply to your last message; It has nothing to do with Office for Mac, but only with the migration.