The point about the quote was when Solaris and BSDs were all doing special treatment of threads (LWPs/LKWT) for M:N threading, Linux since day one started with

The point about the quote was when Solaris and BSDs were all doing special treatment of threads (LWPs/LKWT) for M:N threading, Linux since day one started with treating threads just like processes. The changes to special treat threads to solve problems (clean up manager threads hackery, signal handling improvments, clone syscall improvements, PID semantics etc.) came in later with NPTL as you said but by that time Solaris 9 had already adopted a 1:1 threading model.