Blackmail consists of making an unwarranted demand with menaces with a view to making a gain or causing a loss.
This article seems to focus on ANY demand - your credit card 'threatening' to release information about your non-payment, for example. That is part of your agreement. That is not unwarranted. That is not blackmail.
Heres some clarification with case law (again, this is UK): http://www.e-lawresources.co.uk/Blackmail.php
> Credit cards charge unreasonable rates because there is no collateral. If you don’t pay, they can harass you, and damage your reputation via credit reports, but mostly, as long as you don’t mind losing access to credit, you can run the no-pay strategy and it will work.
> In a legal blackmail world, that credit card company would then seek out damaging information about you, to try and get you to pay. Since you would often be unable to pay, that information would often get released. Other times, you would end up lying or stealing to get the money.
A demand is unwarranted unless:
(a) that they had reasonable grounds for making the demand
(b) that the use of menaces is a proper means of reinforcing the demand.
i.e. the use of "menaces" needs to be proper. In this case, their contract is the proper means of enforcement. Digging up additional "dirt" not covered/mentioned in the relationship would be considered improper, and is therefore blackmail.