I think they are confusing speculation with reality.
The USCG lawyers are sending letters to people who are not guilty of anything (not until they are found/proven guilty).
They are only asserting that they are guilty.
Now they are suing someone for making it possible for the defendants to contest their speculation and requiring them to actually prove guilt in a court of law.
The people they are threatening owe them nothing unless found guilty and someone enabling them to contest their speculation even less.
Gaming the legal system in this way shows that their intent is to extort money using threatening letters with dollar amounts calculated to be cheaper than mounting a defense (as a zero sum game) not prove guilt.
Not too much different from "you have a nice place here, I wouldn't want anything bad to happen to it".
