that makes more sense, someone on silverlight. silverlight isn't the 17th shard, it's just a city in the cognitive realm where a lot of cosmere aware people go.
or maybe it could be a world hopper nalthian who is familiar with both planets and knows about the cognitive realm stuff. But it could always be Khriss or Nazh asking Hoid about stuff.
guys this is quite obviously being told to someone on Roshar by the indubitable Hoidius. I mean who else would use ritual oils in that way? Also someone cals Yuri (or whatever her name was) Warden NIMI. Szeth calls Nightblood sword-nimi! IS THIS THE SILENCE DIVINE!!!