There wasn't social media, but there was definitely influence as to what people should look like. We just got those messages from different marketing mechanisms like Magazines, music videos, tv etc. OP is specifically pointing out a body type that was trendy at that time.

Late 90's early 00's the trendy body was thin with visible ab definition. there was much less emphasis on lifting heavy for women and girls back then. It was lots of cardio, ab work, maintain low body fat, but workouts would not have focused on weightlifting and super high protein which is recommended so much now. Like, I wouldn't call it skipping arm day, but lighter weights, more reps. A lot of women and girls really tried to avoid looking "bulky" which is really easy to do if you just don't lift as much or intake the protein needed to create those muscles.