It likely wasn't robbing but you really have to watch the entrance for a while to make sure. Sounds like a busy hive. I have one like that right now. It's the only one that still beards at night even in this cooler weather. If you went by it around mid-afternoon, you'd think robbing or even swarming. A few hours later, things are quieter. By the way, if it was robbers, you wouldn't have screened them in unless you screened the entrance as well. If you do suspect robbers, try a robber screen. They work pretty good. If you're really not sure about robbing, screen them in at night and then go out in the morning. If you have bees heading straight for the hive, they're not paying a social visit...they're robbing. Then, you'll know!