Don't you think it would be strange, if Chelsea couldn't compete financially, given what has happened since the takeover? How many players, have Chelsea has in their academy/youth teams, that have ultimately either not fulfilled their potential? ended up being loaned out, a lot of times, then moved on?
He may well have been promised a pathway to the first team. Hence his recent involvement. He turns 17 this month and can sign a professional contract. He likely needed to be convinced before signing it.