We see that Raj starts trying to flirt and woo Simran in first meet itself in Dilwale Dulhania Le Jayenge. That time, he didn't had any feelings for Simran. And later he tries to woo her friend and flirt her. So was he genuinely in love for Simran and trying to make her jealous. So he is playboy kind of person, who tries to impress every girl before meeting Simran.
Whether or not he was a playboy is hard to tell, because there is nothing definitive told in the story about Raj's backstory, but it is certainly suggested that he was a guy who could easily flirt with girls and certainly goes after them.
Look at this song and start watching from 2:43. Basically this song introduces the character Raj.
It certainly suggests that the word playboy would not be wrong for him. Additionally what you said is also very indicative of the same thing that upon meeting Simran, he instantly starts to flirt with her and tries to woo her.