The thing to remember is that we're not actually seeing authorial narration in those memories; we're seeing Harry POV. *Harry* is the one who sees nine-year-old Snape as greedy (and Snape); Harry, who's hated him for seven years and who for most of the last couple of years would rather have killed Snape than Voldemort. So strike that greedy comment out from the record. It's only a stab of hatred from the Boy-Who-(Didn't)-Love.