You should probably start your comment with "I'm not a lawyer."
There's a reason that legal research is hard.
But to briefly address your points-
1. Is there "a US law" against receiving unsolicited product."
First, there is no "US law." The US is a law of many jurisdictions- the main two that most people are concerned about are STATE and FEDERAL. So when people look this up, they often completely misunderstand the issue. If something is
given to you (an unsolicited gift, for example) then you have no obligation to return it under federal law (interstate commerce). This doesn't necessarily mean that you are okay under state law, nor does it mean that you are free from civil action. But more importantly, people are asking this question in the context of the rise of scams and/or free products directly sent to them. This is all about people who get sent scam merchandise and are then ordered to pay for it. You can't use this if, for example, a product is addressed to someone else. Or if you bought stolen or counterfeit merchandise. Or if the goods are illegal ("Hey, officer, I know I got a brick of cocaine, but it was unsolicited product! You're cool with that, right?"). Or if there are any number of state laws that you might be violating.
2. The receiver was fine to stream the product since the streamer was not in privity with Hasbro.
Again, this isn't necessarily true. There is such a thing as a trade secrets act. Given that the streamer knew that or had reason to know that the trade secret was acquired by improper means, there is no requirement of privity. That's just off the top of my head- most states have some version of this. But the short version of this is that you don't need to be in privity or have an NDA to be in trouble.
3. Hasbro will be in legal trouble for sending agents to collect the cards.
No. Wishful thinking doesn't make something true. The agents of the corporation made a demand for the return of the product, and it was voluntarily returned.