I'm not your attorney, and even if I were, I don't have enough facts to advise you. I can say, however, that this smells like a shake-down. Assuming that the online stream in question was a copyright-infringing public performance (and I'm not saying it is), I've never heard of a member of the audience being sued for watching it. The exclusive right of the copyright holder extends to the right to perform the work publicly, not to watching a public performance.

Consider the analogy: If I sneak into a theater to watch a movie without paying, it is not copyright infringement. (I may be in legal trouble for trespass, or theft of services from the theater owner, but not for copyright infringement.) If I pay a ticket to watch a movie and it turned out that the theater owner was showing it illegally, it would be the theater owner who would be in trouble, not the audience (assuming that the audience was not in on it).

The problem with shake-downs is that the culprits hope you will decide it is cheaper to pay them than to pay a lawyer to defend your right not to. Good luck. It can be a very unsettling feeling to take the risk that some idiot will go ahead and sue you. Rather than hire your own lawyer, you might want to consider speaking with whatever government office in NH handles consumer fraud and abuse. It strikes me that some Attorneys General might not take kindly to someone threatening litigation over a baseless claim, but I'm not in a position to tell you it is baseless. Best seek good local advice.

Adding to Mr. Mitchell's response, if you do end up wanting to talk with someone, some of the best intellectual property lawyers in the world are right there in New Hampshire at the Univ. of NH School of Law (formerly known as Franklin Pierce Law Center, which is my alma mater) in Concord, NH. Call their IP clinic up to see if you qualify as a client, then show them the email and pick their brains.

If you don't qualify as a client for the IP Law Clinic (it's income-dependent, I believe), give me a call and I will happily give you a couple of referrals to some very good NH IP attorneys. You can find my contact info at www.ipattorneyfirm.com .