I have never had that experience myself, so I can only speculate on what is happening. Please remember: this is entirely a speculation!
The third eye is part of the path of the Governor Vessel meridian, and it connects the perineum/coccyx to the third eye. The Conception Vessel has similar beginning and end points, but it runs down the front of the body. What your boyfriend may be experiencing is prana (or chi) flow along these nadis (meridians).
Kundalini yoga is designed to wake up prana and get it moving. Even more important however is to make sure that the channels are open and ready for the energy to flow. This is often the goal of chakra work: you don't want to pump a lot of energy through a closed channel - that can create all sorts of damage. I hope you and your boyfriend seek advice from a seasoned teacher if this experience of prana moving continues. The teacher should be able to guide you further.
Dr Motoyama recommends that the first chakra we should open is the third eye. Once that is opened, we will have the wisdom to proceed with opening the lower chakras, safely.
If the experience gets to be uncomfortable, your boyfriend may want to do the Micro-Cosmic Orbit, to ground and centre the energies. See the section describing how to do this in YinSights:
http://www.yinyoga.com/ys2_2.2.7.3.4_mi ... _orbit.php
Again, since I have not experienced this personally and am not your boyfriend's teacher, please don't take anything I am suggesting as direction. It is all speculation on my part, not knowing your boyfriend.
cheers
Bernie