Rockstar Social Club code may refer to PC version Red Dead Redemption 2
Code from Rockstars Social Club website contains the text RDR2_PC_Accomplishments. That seems to refer to a PC version of the game. Accomplishments are the equivalent of Xbox Achievements and PlayStation Throphies.
Rockstar uses the term Accomplishments on its Social Club network when players achieve certain goals in games. The source code with the reference to RDR2_PC was noticed by a game level designer on Twitter. The reference is online and can be seen in code found on a website associated with Rockstars Social Club. In addition to RDR2_PC, there are also references to RDR2_PS4 and RDR2_XBOX.
Red Dead Redemption 2 appeared at the end of last year for the Xbox One and the PlayStation 4. Rockstar has never said anything about a possible PC version. The first part was never released for PC. However, GTA V did come to PC, after the game was first exclusive to consoles for more than a year.