They're quoting the KJV of the Bible, it's incorrect in modern language, but I found this:
"It's an archaic use of English which conjugates verbs of motion with be in present perfect, in much the same way as French still does. The statement is the equivalent of "Christ has risen" and is stating a present-perfect fact."
I think the simple explanation is they suck at grammar and write "He's risen" not recognizing the 's with the auxiliary verb means has.
I actually think they are using "risen" as an adjective… Descriptive of a person who has risen from the dead. See, "He is fucked"
If that is the case, the grammar is fine.
They're quoting the KJV of the Bible, it's incorrect in modern language, but I found this:
"It's an archaic use of English which conjugates verbs of motion with be in present perfect, in much the same way as French still does. The statement is the equivalent of "Christ has risen" and is stating a present-perfect fact."
https://english.stackexchange.com/questions/237348/is-he-is-risen-correct