What was the wind like? Was thinking it may be a race with 2 fast bits and 2 slow bits but that's not visible in your splits. I did one in particular like that a group of 15-20 into the wind and then a big split with the tail wind smaller groups up and split again for the final leg.
It was marginally harder into the wind but not significantly so - also the corners don't fall in nice places (ie it's not out, back, out, back; its more like 600m out, 2k, 2k, 2k, 1400m in...)
On a windy day it would be a horrible race.
They have clearly moved the start again since I last did it. It got far to depressing for me to carry on doing once I slowed down. Did it once with high tide big waves if you were unlucky you got soaked when a wave hit the wall hard. In the day it had the advantage of being on every month so you could know where you were fitness wise. Now with a park run every Saturday it's easy to have something to use as a benchmark if you want to do that.
Your 1st km was silly! I went thru in 3:30 in my 5km PB and was slowing down even then as was clearly too fast! Get the pacing right....