Partially correct. EdgeHTML was in IE11, but wasn't a renamed MSHTML (check your system32, you'll see both DLLs in Win10). It's a departure from MSHTML that's been seriously changed, lots of cruft removed and a lot of interop added.

Fun anecdote - last week someone at Steam wrote one of the sale pages using entirely -webkit- prefixes. It showed up blank in Forefox, but rendered fine in Spartan and Chrome.