Completely different. Really cool to see a quickly working demo but it's using a cut down version of the Signal protocol which I abandoned early on because it makes private group conversations extremely hard / if not impossible.  

 Can MLS be done using only nostr-tools primitives like DH and hkdf? 

 No. Not currently and maybe never. 

 Why? Signal and OMEMO (Jabber) both support private group chats.