CPU/mobo temps cooler after ticking PWM from DC on intake fan? 2000rpm down to 1000.

How does this make since? I like it and am not changing it. I did it because my intake fans were super annoyingly loud.

Wound up getting a 3000rpm Noctua because it has a lot of stuff to pass through on intake so wanted a good strong pull of air.

Anyways I ticked it to PWM because it knocked it down to 1000 rpms instead of the 2000 it normally ran on DC.

Now my cpu and mobo temps are 2-3 degrees cooler.

Just curious if this is normal and if so why?