hCG trigger 20 minutes after IUI???

Hello Ladies,

I've had my second IUI a week ago which seemed to be a bit unorthodox but I hope it still made some sense.
I ovulate on my own, I have cycles like clockwork. I had my natural LH surge oct 21 at noon (I use opk sticks.) .
24 hours later, oct 22 at noon IUI was done. Then... 20 minutes after the IUI I got a hCG trigger.
On day the of the IUI I had one mature follie, measured 22mm.

I asked the nurse; it was meant to achieve a perfect timing for ovulation and not to boost progesterone.
This procedure just seems odd to me. Does that make any sense to you?

Me: 36, unexplained infertility
DH: 37 perfect
TTC: 6 years

#1 IUI: Sep 24 - failed (natural cycle)
#2 IUI: Oct 22 - ??? (hCG trigger)