When broodlords a-move,the range is indeed 10.
But if BL attacks a target,the range can be nearly 13.
You can watch this video below.It's in Chinese ,but you don't need to listen to it,just watch.
Go to 1:48.A tank is in siege mode,its range is 13 and there's a circle marking the range.Then let a BL attack the tank,you can see the BL starts its attack outside the circle,that's to say,the BL's range is more than 13 when targeting a unit.
From 2:46,the video shows the difference between BL's a-move and attacking target.Thor's anti-air range is 11,which is more than BL's range.But thors can't return fire when BLs just target one thor.