It's actually sodium chloride--table salt--but I suspect Hairguru already knows that.
I had this exact same question when I started out. I posed it on the non-hair board to some members with chemistry backgrounds, in addition to using my own limited chemical knowledge from college. Unfortunately, the two opinions were different. The "chemist" said: If it says to avoid sodium chloride, then just avoid sodium chloride." Well, I already knew that "sodium + something else" does not necessarily = "salt" and doesn't have the same chemical properties as sodium chloride, but I still wasn't convinced. So, I decided to err on the side of caution and avoid anything containing the word sodium.
I'm still experimenting with potassium chloride, as it is chemically similar and is even used in many of the same applications as sodium chloride. So far, so good, though.
I'm starting to wonder if the cumulative effects of BKT truly "wash" or "wear" out of your hair. It's been almost 6 months since my last full-head, and my curls are showing no sign of reverting. I've washed my hair with a clarifying shampoo every month since then for root applications. I wonder if you do it as frequently as I do, it affects the hair permanently, which would be totally fine with me!
Anyway, sorry I don't have anything more definitive; maybe someone else will.