It's not blackmail in the first place. There were no secrets to reveal since everything was published online, and it's legal to sue and report a possible crime. Speculating about the consequences doesn't make it blackmail.
The vast majority of neurotypical English-speaking adults would have no difficulty categorising it as a veiled threat. Note the strong consensus in this comments section.
The message has two parts - the response that X wants from Y, and the possible negative consequences for Y. The proximity of the two parts makes the implied link clear (to most people, anyway).
I assure you that 99% of judges and prosecutors would recognise this as blackmail (modulo variance in different countries' legal definitions of the crime).
