There is a bit of nuance here. IE today still isn’t decoupled from Windows. MS has been shoving it into an ever smaller corner of Windows but IE is the OS provided webview for a lot of old crusty applications that needed to render HTML.
What they’re talking about is IE the OS component didn’t mean that IE the user-facing general-purpose browser had to be the default.
I thought that argument was rejected already in 2001[0].
[0]: https://en.wikipedia.org/wiki/United_States_v._Microsoft_Cor....
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(edited to fix link formatting)