I'm not sure why you are bringing this up but, of course, vicar of the Son of God, means, vicarious Christ, acting in the place of, or instead of, Christ.
a : serving instead of someone or something else b : that has been delegated <vicarious authority>
: performed or suffered by one person as a substitute for another or to the benefit or advantage of another : substitutionary <a vicarious sacrifice>
This is the very definition of antichrist. The 'anti' in antichrist means 'instead of.'
And, of course, they knew this when they gave him that title, because, unlike us, they could speak Latin, Greek, and Hebrew.
1 John 2:18
Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time.