Exactly. Having the opposing team read out the cards prevents information transfer. Bridge has controls like this already. You aren't allowed to lie about what your bid means, for example. If a player is confused about a bid from the player on their right, they are allowed to ask the player on the left what it means and they have to honestly answer.

Or just buy a set of playing cards with braille on them (even if he didn't read braille, it would be easy enough to learn 4 suits and 13 ranks).

FWIW, Braille doesn’t have a super high literacy rate among the blind. It depends on the age, education history, economic status, etc.

You would have thought Braille for cards is pretty trivial to learn - there's only 13 values and 4 suits.

I understand what a couple Braille symbols mean, and I for the life of me can not feel them out of a line of other shapes. It’s more than knowing the translation. You are calibrating your finger, memorizing and translating, and developing that focus.