Sharp line no, but there is a line, and that line makes up the difference between a cohesive experience and an incoherent one.
Now, Roleplay is interactive, no doubt, but it isn't mechanical and fundamentally can't be when you get down to it (hence why social mechanics always tend to fail), and without mechanics, you're not actually creating a game.
Sharp or fuzzy line, if you can say "Roleplay" is a separate thing from playing a roleplaying game, that you must disengage from the game itself, in order to really roleplay, then I have to disagree. The playing of a roleplaying game is roleplaying. You do not need to pause the game and override it's resolution systems to roleplay. I mean, it may just be a bad game and avoiding it's resolution systems may be a good idea, but it's not necessary to do so in order to roleplay.
Rather, the line, there, between roleplaying by playing the game and disengaging from the game to roleplay without reference to rules or mechanics, is the line between TTRPG and Freestyle RP. Both are roleplaying, one is a game, the other is not, it's an exercise in improvisation or some such.
To me, a key litmus test for roleplaying is that you can assume a role that is
different from yourself. In most RPGs, assuming a role that is taller, smaller, stronger, faster, tougher, more athletic, agile, deft, or even possesses supernatural power, is mechanically covered in robust ways, and blithely accepted in even the most radical corners of the hobby. While assuming a role of someone, more clever, cunning, knowledgeable, intelligent, persuasive, charismatic, diplomatic, or/and astute (or,
less of any of those things) gets pretty fraught.
Mechanics can generate stories all on their own, without needing to force and hamfist the narrative.
So in that light, I would judge Story First/Story Now type stuff as being a fundamental misuse of the medium, which yet again loops back to my comments on innovation and how mechanics are being held back. Better mechanics will do more for a game to tell stories than trying to force it will.
And that sounds like a completely different sentiment than the above.
