my friend consistently gets about 3/4 to 1 ounce from his fluro plants. Its not as firm as what I see with HPS but he kept the lights super close, nice ventillation. They get topped, about 3-4 weeks of veg, and 7-8 flowering. Cant remember the ferts but they are an organic, aparantly cant burn. These plants are about 1.5 feet tall and equally wide.

There could be tons of factors, but I would bet on not enough light that is not close enough, irregular lighting, the wrong kind of trimming, or the wrong amount of flowering.

For reference, I have seen a few 5 foot indoor plants that produced 1/4 to a half pound each. Not to discourage your friend, but sounds like the environment wasnt ideal.