The best piece of advice I ever received was that you ride with BOTH reins.
I tend to be very mechanical, so if you tell me to hold my outside rein, I will. That’s not correct. The outside rein is your support system. Your horse must learn to maintain a steady contact on the outside rein, yes, but that doesn’t mean you have a death grip on it’s mouth. For me, I like to maintain my contact with my ring finger, then I can close my middle finger and index finger to increase contact.
I will echo that OTTB’s aren’t traditional. They’ve already been trained, now you have to teach them something entirely different. They are taught to pull against the contact. For my own Thoroughbred, I had to give the outside rein intially to teach him contact was there to help him, not rush him.
i would ask for clarification. There is nothing wrong with saying, hey I’m confused - it was my understanding that i was supposed to do “this” why are you asking me to do “that.” What will “that” accomplish. If it turns into an entire lesson, who cares… it will help you understand.
Unpopular opinion, I lean more towards the new BO. I have a hard time believing a 4 y/o OTTB would have the capacity to turn on the outside rein until you teach it how to carry contact on the outside rein. Should you ride like that always? No way. It may be appropriate for this stage of the game.
Don’t be afraid to marry the two ideas together either. Riding is feel. Trying to communicate feel universally is very difficult and teaching styles can be very different. It’s our responsibility to navigate the gray area and figure out what works well for our horse individually. New BO might be asking you to throw the contact away in an effort to encourage your horse to fill the outside rein (think of it like steering a bicycle or visualize train tracks). I don’t know… but I would ask!