To be clear, it’s black salt which is possibly in sand sized particles not black beach sand. So he doesn’t need to worry about leaving grit in the puffed rice.
Last year I got into a bit of a habit of eating bhel puri for breakfast - took a while before I realised probably why it occurred to me as something to do, that bhel is basically 'Rice Krispies' or similar. So for someone who doesn't like milk, (on its own/in large quantity like that) but loves spice, bhel puri is the ultimate breakfast cereal. :)
https://en.wikipedia.org/wiki/Kala_namak