He probably just saw that SN was such a fancy chemical word that caused Metho-anemia and latched onto it.
He actually got the idea from the RTD group CKW in The Netherlands. There was huge publicity when they announced they had found a possible "Pill of Drion", but they didn't release the information because it was too early and it hadn't been investigated. They didn't want people rushing out and buying it, then using it.
PN, being part of the inner RTD circle at the time, found out what it was. He immediately cobbled together a new section on lethal salts in the PPeH, and spruiked it to the world. Sales to the PPeH went through the roof, breaking all records.
He admits his first entry in the PPeH was flawed. What he simply doesn't see is that when he makes an announcement, enough people trust him to believe him. They hang on to his every word. These are vulnerable people, many elderly, with a terminal illness or chronic pain. No-one knows how many people would have died with SN. No-one knows if it was a peaceful death, or as one eminent Dutch medical person said, a "horrible death".
It works, definitely. Anyone here has the right to choose it, if they wish. The important thing is that the choice is made with full access to the known facts and unknown possibilities.