It is perfectly clear that you are correct because trying to tell anyone about confidential subpoenas could be illegal.
When it requires so much "reading between the lines" that even this community doesn't have a strong consensus on whether this is being (illegally) communicated or not, I think it's plausibly deniable, but IANAL. Contrast with well-known canaries.
Canaries that are well known would just become normal communication and thus illegal under a non-disclosure. It's just going to get worse lol.