There's another episode from Gaming Historian specifically for Tengen:
https://www.youtube.com/watch?v=fLA_d9q6ySs
It talks about how Atari abuses the copyright system to gain access to Nintendo’s protection system source code.
Nope, while Nintendo definitely abused copyright law doesn't mean Atari/Tengen is in the clear. They specifically requested the lockout code fron the US Copyright Office under the pretense that they'll be suing Nintendo.