They licensed Spider Software's TCP/IP stack. And you have no knowledge that Spider leveraged BSD code. You're probably too young to remember, but there were many vendors making TCP/IP stacks back in those days. Some based on pre-existing stacks, others from the ground up.
https://ia904500.us.archive.org/view_archive.php?archive=/23...
TCPIP.SYS is the TCP/IP stack in Windows.
I'm unsure as to why you're making unsubstantiated claims and sticking with them. You have zero proof that the claims you're making are true. I'd love to have the source for Spider's TCP or at least have a contact that worked on the stack to ask, it's interesting history. I don't care one way or another, it was a very temporary stack that didn't make it into 3.5 where the entire stack architecture changed (no longer based on SysV STREAMS).