The main gates usually only happens 10-15 minutes before the park's official opening time and then in most cases you are "held" at a secondary location for the actual rope drop activities. Rope drop generally happens right at about the schedule park opening time, but if you are just getting to the gates then you will be behind anyone who was there when they let people into the park earlier.
On rare occassions they do just open things up early, but there's no way to predict that and in my experience it doesn't happen often.
Is it possible that you may have hit a morning EMH day at the park's scheduled opening time without realizing it? In that case, resort guests would have been allowed in an hour early and you definitely would see people in the park and active if you arrived at the scheduled opening or just before.
Unless we're doing a morning EMH, we're typically at the park at least 30 minutes before scheduled opening and I've never arrived to find the park open and operating.