He was 100% lying.
On the 24th of June he posted a story on Instagram denying he had signed with the club
"Hey guys just a quick update on the conract situation,” Capewell said "Obviously the media are reporting that I’ve signed – I haven’t signed anywhere." “I won’t be making any decisions until after Origin. I’ve got bigger fish to fry this week on Sunday. “I’m gonna get out there and give it to the Blues. Thanks for all the messages of support anyway. Let’s go this weekend, go the Maroons.”"
Capewell to Join Broncos from 2022
Author
broncos.com.au
Timestamp Thu 1 Jul 2021, 11:29 AM
So exactly 7 days later it's announced. Given they have to lodge them with the NRL and it has to be approved by the salary cap auditor, there's no way that entire process wasn't already done and he had not already signed on.