No, Core happened before Mono integrated in to the Standard platform. I believe Mono started to use the open sourced components of Core/.Net framework to replac

No, Core happened before Mono integrated in to the Standard platform. I believe Mono started to use the open sourced components of Core/.Net framework to replace some of their components.That might be where the confusion lies. Then at some point after that, Microsoft acquired Xamarin and opened the Mono/Xamarin platforms fully (the Mono runtime used to have tricky licensing that meant that embedding it required a commercial license.)