This is a classic example of why sparring should never be System A vs System A. Most martial arts schools fight against the same style so students are only used to fighting against the same system that they train. This becomes a big problem when fighting against another system. I train Jow Ga Kung Fu and I don't like sparring against other Jow Ga students unless they don't know how to use Jow Ga. My theory is simple. If Traditional Martial Arts is for beating people, then most likely it's going to be people who don't train under the same system. For example, what's the possibility that you will get into a street fight against someone else who knows Wing Chun? If you were to fight 10 people in the street today, then it would be unlikely that you will fight against another Wing Chun practitioner. So if that's the reality, then it's best to train to fight against the type of people you may actually get into a fight with.
I could fight 300 people from the street and there's a good possibility that none will be a Jow Ga practitioner, so if that's the reality then it doesn't make sense for me to learn how to fight against Jow Ga. I have to learn how to fight against everything else starting with the most common which is probably just a regular street brawler.
If a martial arts master stated he didn't want other to know how the system works because then they will analyze it and then learn how to defeat it, then that makes sense to me. Even the old Kung Fu movies took that approach. BJJ used to take down tons of strikers, but a more MMA fighters become familiar with BJJ, the take downs don't come as easily as they used to. Fighters learned how to escape them and remain on their feet. When BJJ was new, very few knew how to deal with that. So not wanting to show it in fear that someone will learn how to defeat it is a legitimate reason, but it's not a good one as it limits the development of a system. When someone figures out your ability, then you just have to get better at what you do, which will in turn help develop the system into something better.
BJJ figured out strike and in return MMA Strikers got better with striking and better with escaping BJJ. MMA striking is a lot better and more diverse than it was in the first MMA. This would not have happened if it was only "System A vs System A" Unfortunately there's a lot of Kung Fu practitioners that don't take this approach.