At that early time in the development of RPGs there was little understanding of what could in principle constitute different types of play. I mean, people were just starting to explore possible rules structures that produced fairly D&D-like game processes. Sometimes something like the Streetwise skill in Traveller would appear (where the player gets to say "Tell me where to find the illegal guns." and the GM is supposed to say something like "go talk to Igor over there in the back alley." not "no such thing exists."). I don't think Mark Miller had some great revelation about Narrativist play there, or at best he just imagined it as a 'neat trick' that solved one specific problem in an otherwise pretty Trad game.
Traveller's chargen is also an interesting case, with its myriad of choices, but notice that few of them amount to "build exactly this sort of character." Its more like the player suggests things. Still, it produces a strong indication of interest in how they want to play. So the players could make a bunch of Soldier characters and push the game in the direction of mercenary missions and such, or Merchants and Scouts, and go for a game focused on travel and exploration. The Patron system, TAS, and trading subsystems give them further leverage, since they are all designed to be invoked by the players (at least by implication, if not explicitly).
Those are reasons I note it as being a bit harder to pigeonhole as an 'Old School' game, BUT that being said, IME (I think my Traveller books are first printings, lol) the game was mostly played in a fairly trad mode. Either the GM ran one of the modules, or constructed some sort of adventure. OTOH you really could play in a pretty Low Myth kind of way, which we did in some of our later campaigns, where the players were just dropped at a starport or something in Scene 1, and everything beyond that resulted from interacting with those subsystems. Even then it was likely the GM would drop leads to some pregen adventures sometimes.
Its also telling, as
@pemerton has noted, that later editions of the books tended to tweak the language back in the direction of more GM-centered play with fictional authority concentrated more in their lap. Even if you were playing the mid '80s text though, the option to go Low Myth is still there, and the various supplements seem to actually increase the players ability to get the characters they really want (although the luck of rolling up your ability scores is still pretty substantial).