I have no idea! Speculating baselessly: a country might choose to hold excess foreign reserves without publicly disclaiming them when it lacks confidence in it

I have no idea! Speculating baselessly: a country might choose to hold excess foreign reserves without publicly disclaiming them when it lacks confidence in its own currency or economy, or if it foresees global market upsets (e.g. wars) that would make their local currency less desirable for international trade. I agree with your point about eroding trust: it’s hard to think of a reason to do this that would be worth it.