No, kbin.cafe is not run by the same person that runs kbin.social; here's a post by the owner of kbin.cafe and @ernest is the owner of kbin.social and the main developer of kbin. As you mentioned, kbin works similar to an email service, so different kbins (and lemmys and mastodons) can communicate with each other.
That is really cool. I dont go online often but I like that they can all communicate.
Just wanted to let you know that this is the best thing I’ve read on the fediverse, and by a fair margin at that.