I would suggest that you actually take your own advice and get more information yourself.
No license can force you to release your code. Nope, not even GPL.
Instead, what a rights holder can do, is sue for damages for the copyright theft, for not following the license. They can't force you to follow the license. Instead, they can say that you didn't follow it, therefore you stole the code, and owe money to them, for stealing the code, depending on how much the code is worth.
The only thing that GPL does, is it gives people permission to use the works, in exchange for releasing code. But, if you infringe, the damages do not depend on whatever the license was, or whatever request the license makes.
To use an example someone else gave, of the "first born child" license, imagine someone writes a simple binary search function, and puts out a license that gives it out for free, in exchange for paying them some absurd price. EX: the joke of the first born child, but more seriously, lets say the license was "1 million dollars".
If someone stole that binary search, couple line function code, and it went to court, they absolutely would not own them 1 million dollars, even though thats what the license said.
Instead, they would owe the rights holders damages. And chances are, a couple line binary search function, or some other example that you could think of, would only be worth a small amount.
And even though the license said "This code is worth 1 million dollars, and you owe us that money if you use it!", it is not true that anyone would owe them a million dollars. Instead they would only owe them damages, which would not be anywhere close to 1 million dollars.
