I logged into dropbox from ipad, i saw files that didn't even belong to me

So basically on my ipad i logged into dropbox after a long while of not using it, and saw files that didn't belong to me, im not sure but they look like files that might have belonged to a professor whose class i was in years ago, i'm not 100% sure, but i then logged in to dropbox through my phone and later see those files disappeared.  Why is it i saw those files in the first place, and are my own files pretty much safe from being seen by other people, some of those files are private im worried my being able to see files that didn't belong to me might mean someone else could get to and see files that are mine.