Their lack of (supposed: I don't know how well read either mathematician is in philosophy) philosophical credentials might justifiably invite scepticism.
But surely we can only dismiss this if their argument has a flaw. And the burden of disproof is on us, not them.
They seem to think free will is a part of physics, not philosophy, and reductionist physics at that. They didn't address any actual problems in the field. They missed the point. That is a flaw in their non-argument.
The burden is on them to say what is a problem in the field they want to address, to know something about the history of the problem, other candidate solutions to it, and how their solution differs, and then say what the answer is. They simply haven't done that.
What they've done is define a property, tack the name "free will" onto it because it resembles some people's definitions of free will, and prove some things about it. If their math is sound, then good for them. Whether this is applicable to anything is certainly up for discussion, of course.
They are trying to prove stuff about free will, but have no expertise on the question of what free will is.
If you disagree, please post a comment saying why. I'd like to hear it.