His deal with Penrith for this year is $780k. Panthers will have already paid $100k of that.
I agree it seems frivilous that they'd release him early, but it's also very easy to see now why he has decided his future is elsewhere.
If you are a key part of a spine that has delivered 3 straight titles, and you're offered $70k a year more following those performances, knowing the salaries of others in the team, I would be out too.
Even more so when you consider the commentary from the CEO and Coach in the off season.