No contractual reason to delay the announcement. Most of our signings this summer won't have been immediate but that didn't stop the press release.
If he is contracted then he wouldn't be able to sign until said contract has elapsed. Otherwise it would be a breach of contract and he or the club would incur fines. Maybe his club really don't want him to go.
The fact that we haven't seen or heard of him before means maybe a non league player with oodles of talent and we are giving him his big break at a higher level.