I've used stud chains on a TON of horses. Some for control, some for other reasons. I would not necessarily be concerned about it. I have my own horse that I used one on regularly, while he's not a beginner's horse he's not difficult to handle, but he is strong and if grazing for example I'd rather just not deal with corrections constantly. Does he *NEED* one no. I've also worked at a barn that all the horses had stud chains. If I have a lead with a chain I will likely use it. A foot long (or w/e) piece of metal waving around isn't always pretty, it's not harsh to just have it sitting there if you put it on properly. Sort of it's there if you need it if not then fine, like holding a crop when you ride.
The fact the horse bit you the first time meeting is a red flag.
It sure sounds like an "actual stud chain" it may or may not have been attached properly (Thanks for pointing that out DC, pet peeve!) but as I said it's not necessarily a red flag. I'd just ask why they have a chain on him. And DO make pointed questions, it's ok and expected even.