If this is correct, and I assume it is, why?
I don't know why, but it is correct.
Years ago I was cycling 200-300km/week. My resting heart rate was 45 and bp was 140/90. I was extremely fit. My cycling mate's wife, a nurse, started testing our bp immediately on our return and diastolic was always lower - 70-80. My mates was much lower, as he has almost hypotension - feints if he stands up quickly.
When my bp was in its normal range, my GP always kept an eye on it, because "it's borderline high for a bloke your age." When I retired (from both work and cycling), diastolic dropped slightly, but sadly, he informed me that they'd also redefined normal.