I think I’d put it down to a number of factors:
a) some saying that simply cos they want it to be so
b) some saying it cos we’ve signed players before who have been viewed as ‘underwhelming’ in some ways at the time but who have gone on to be really important and effective parts of our success under Pep, so feel this can happen again here, and
c) some saying it cos they genuinely believe he has shown great play at Chelsea/ internationally.
For those 3 reasons I’m honestly not as surprised as you.