Coaches- help interpret my HM HR data

I'm 53yo male, 6ft/172# with approx maxHR 182.  No real run background except 3 yrs of tri.  Last Fall my est run LTHR by field test was ~150bpm.  My training has been run focused this year with workouts based on that 150 LTHR.  Last month I did sprint tri with run HR 156 bpm for the 5k (which I prob could have run a bit faster).  My Spring's A-race was HM yesterday (2hr goal) & it went well. Started slow (34sec>goal pace 1st 2mi), & gradually increased pace throughout race.  Ran 1:57 (PB by >5min) & finished strong.  Ran 5+min neg split & last 1.1mi @ 7:50 pace (fastest of my race).  Though I wore my Forerunner for pacing, I ignored HR & ran by RPE.  Didn't hurt much until last 1.5-2mi of race.

Looking at the Forerunner's data has me scratching my head. Overall the data looks solid with minimal artifact.  As I expected from my efforts, pace & HR gradually trended up as race went on without fade at the end. What confuses me is HR ave was 158, with lowest mile ave 146 (mile 1 of course), and peak HR 175 @ finish line.  I train by HR, but NEVER would have guessed my event's ave HR was that high.  Does that suggest my run LTHR is really 158+???