Earlier quoted context omitted.
But the claimed phenomenon here is that it's (almost) always easier for you to come up with a solution to someone else's problem than for them to do so, not just that some problems are easier for one person than another. There are problems with this claim, I think, but the absence of free will is not an explanation, or at best just reduces it to the question of why, granting the claim, the determinism (almost) always…
The outside with the solution doesn't have to live with the result and likely doesn't comprehend the un-stated nuances of the situation. That makes problem solving easy.
Yes, that's the kind of thing I had in mind by saying that I thought that there were problems with the claim.