To me it looks SEVERELY over/under watered, also I would say hes got humidity issues or heat issues in hes grow area as per the leaves nearest to the top of the plant.
That sort of leaf curl and canoeing is what happens when plants are given nutrients too strong or the light is too close or the heat is too high or the humidity is far too high and it could be all things rolled into one.
Does said friend have a weather station in hes grow-area and or a hygrometer to check Relative humidity and temps throughout the day.
It may be that hes feeding too often, using the wrong nutrients for hes medium/soil mix, it could be too cold these are all things I would be checking before he makes any quick decisions.
As it could be a simple matter of getting fans into the area.
Also indoor plants will grow faster than outdoor plants as you are CONTROLLING YOUR ENVIROMENT to replicate and magnify the effects of sunlight.
With the only real differential between indoor and outdoor being you have infinite space outdoors so you can grow a 10ft bush outside, but inside your generally limited to around 7ft.
He may have light leaks out of this cabinet which will also stop flowering.
Granted MJ is a weed, and it will grow anywhere in any conditions (nearly).
but for it to grow at an optimal rate and look beautiful it must be kept inside a controlled environment, it isn't as simple as just hollowing a 3x2 cab and throwing plants under some lights (although that will work) it wont happen in a normal 3 month or so time frame.
I'm not saying or implying you or your friend have no idea about growing MJ, I am simply running through the basics of what could potentially cause the problem as people with more knowledge than me have not yet replied I feel what ive given should shed SOME light.
I swear it's not me. 
