They named their framework ASP.Net MVC, as it is an MVC framework for ASP.Net, The naming isn't that problematic.
Lots of people in the close-minded cult of Microsoft (which does not include all Microsoft devs.) both shorten the name to "MVC" (which isn't necessarily bad in certain contexts) and have little-to-no understanding of what MVC is other than ASP.Net MVC, so both themselves confuse the pattern with the Microsoft product and promote others doing the same thing.
Roughly the same thing happens with Microsoft SQL Server (which becomes just "SQL").
Lots of people in the close-minded cult of Microsoft (which does not include all Microsoft devs.) both shorten the name to "MVC" (which isn't necessarily bad in certain contexts) and have little-to-no understanding of what MVC is other than ASP.Net MVC, so both themselves confuse the pattern with the Microsoft product and promote others doing the same thing.
Roughly the same thing happens with Microsoft SQL Server (which becomes just "SQL").