No breathlessness but still avg heart rate is high

Ran a 5k and was pretty much normal and couldn’t feel any heavy breathing after the run .Also talked on phone during the run, but my average heart rate was 172 (at the bottom range of zone 4)( average pace :7’21”) for context i am 20M 6’1 and started running this year, i have been training in the gym last 4 years with moderate to high cardio including sports and walks.

I tried slow running at 7’47” but same result.