R. Nechemiah expounds this ("he") as referring to the nations, viz. "And he (Titus) will say." Titus, the son of the wife of Vespasian, went into the holy of holies, tore the curtain with a knife, and said "Where is their G-d? If he is G-d, let Him come and fight with me!"
"who ate the fat of their sacrifices." He said: These (Jews) were swindled by Moses, who said to them: Build an altar, sacrifice burnt-offerings upon it, and pour libations upon it, as it is written (Bamidbar 29:4) "The one lamb shall you make in the morning, etc." (all for his own delectation!)