There is no proof of "the" cause of our feeling of free will.

EY has put forward an argument for a cause of our having a sense of free will despite our not, supposedly, having free will.

That doesn't constitute the cause, since believers in free will can explain the sense of free will, in another way, as a correct introspection.

EYs argument is not an argument for the only possible cause of a sense of free will , or of the incoherence of free will.. However an argument for the incoherence (at least naturalitically) of free will needs to be supplied in order to support the intended and advertised solution., that there is a uniquely satisfactory solution to free will which has been missed for centuries,