Can we append sources - even if they are only 'traditional' to this profile?
At the moment it appears that this profile and "Macduff" might be attempting to designate the same extrapolated ancestor.
Their dates don't match by at least a full generation, so I suspect it's two radically different extrapolations. "Duff MacEth" appears to be an attempt to force-graft the MacDuffs onto the Boethe-Lulach-Aed line of Moray.
IMHO if there's a relationship at all, it's collateral, not direct - hence, a line of MacDuffs descending from Giric, the oldest son of Kenneth III, rather than from Boethe, a younger son.
Having a valid senior male line would also explain why Gruoch wasn't "the heiress" to Clan Duff.