You're getting downvoted to hell for a small misunderstanding, and the replies aren't necessarily helping.
NeXT is the reason Apple went with a UNIX-type OS that evolved into OS X, yes.
Linux is also a UNIX-type OS, but is not an ancestor of OS X.
Linux is so popular now that it's easy to identify it with UNIX but historically it's only one of several implementations that work in roughly similar ways.
Other replies are telling you which code OS X was actually descended from.
I never heard that one before. I thought Linux was just a conflation of "Linus" and "Unix", while GNU was a recursive abbreviation of "GNU is Not Unix".
Linux means "Linus's Unix" and the name came from the sysadmin at funet.fi who had to give the kernel a home subdirectory when Linus asked him to host the kernel on an FTP site ..
NeXT is the reason Apple went with a UNIX-type OS that evolved into OS X, yes.
Linux is also a UNIX-type OS, but is not an ancestor of OS X.
Linux is so popular now that it's easy to identify it with UNIX but historically it's only one of several implementations that work in roughly similar ways.
Other replies are telling you which code OS X was actually descended from.