Microsoft decided to rename ASP.NET 5 to ASP.NET Core 1.0. So ASP.NET 5 would be now ASP.NET Core 1.0, .NET Core 5 is now .NET Core 1.0 and Entity Framework 7 is now Entity Framework Core 1.0
Microsoft have been working towards “One ASP.NET” now for years and we’re there. ASP.NET Core is versioned as 1.0 as it’s a near complete rewrite of ASP.NET with many new features and capabilities.
ASP.NET Core 1.0 is not a continuation of ASP.NET 4.6. It is a whole new framework, a side-by-side project which happily lives alongside everything else we know. It is an actual re-write of the current ASP.NET 4.6 framework, but much smaller and a lot more modular.