Perhaps his memory failed as mine did over Wm in Patrick - following your correction I think the Cavendish referernce was in Probate Records concerning his father-in-law's will.

If we wish to give AW the benefit of the doubt, maybe he mis-read a couple of entries in the old original register. I don't even know - Frances may - at how many removes we are operating from the original, if any?
It would seem very unlikely that there would be Cavendish entries that long ago, but of course folk and maybe official etymology had been rife even before this.