The PHB disagrees with you: "Roleplaying is... you as a player determining how your character thinks, acts, and talks."
[MENTION=23751]Maxperson[/MENTION], is your interpretation of the PHB definition of roleplaying that in each instance of role-play the player must make decisions about all three of the named ways the character can react to/interact with its environment, and if any one way is missing it is not roleplaying?
Not really. "You as a player determining how your character thinks, acts, and talks" is synonymous with "You as a player determine how your character thinks, and how your character acts, and how your character talks." And the latter clearly leaves an implicit "if at all" open in each conjunct. Writing it with or - "You as a player determine how your character thinks, or how your character acts, or how your character talks" - generates at least a weak implication that the disjuncts are exclusive, whereas using "and" allows for the fact that it might be one, some or all of the alternatives that a player determines.It is according to your quote.
It doesn't say that roleplaying is "...how your character thinks, acts OR talks.". It uses "and". That use of and means that it requires all three.
The syntax and semantics of "and" and "or" in English is not the same as that of the formal logical operators that go under those labels.
Also, I think 5e is a bit equivocal over what counts as roleplaying. Eg p 66 of the Basic PDF says, "Roleplaying is a part of every aspect of the game, and it comes to the fore during social interactions. Your character’s quirks, mannerisms, and personality influence how interactions resolve." And p 35 says that "if you have inspiration, you can reward another player for good roleplaying".
This is closer towards roleplaying as characterisation than roleplaying as making decisions for one's character, I think. Which is to say that I think the D&D rules might reflect the same tension/ambiguity that we see in the community of players.