Earlier quoted context omitted.
Is this in reference to something that should be linked for those not alive or in the know at the time?
I'm not sure if it was entirely true, but there are stories that after Microsoft bought Hotmail in the mid-90's, they quickly attempted to move them from FreeBSD (?) to Windows NT. But it failed miserably, and they went back to the original stack for another ~decade.
the Solaris bits (storage and routing tables) took far longer - and again iirc the frontend had been rewritten in C# before all the Sun hardware had been decommissioned.