Somewhere in Crime question

Is it just me or is there a date continuity problem in the prologue? The prologue is dated as taking place in 2009 but near the end of the prologue Jack tells his kids he’s going to tell them a “tale about the summer of 1979, twenty years ago, when…” If the setting is currently 2009, 1979 would be THIRTY years ago, not twenty. I get that the crime he tries to solve in 1979 was a twenty-year-old crime (meaning the crime took place in 1959) but the phrasing of this sentence implies that 1979 was twenty years prior to the time of the setting in the prologue. I’m only two chapters into the book but for some reason, I just can’t get past this seeming discontinuity.