I understand that is what they told you but a lb of decent bud will give you around 45 grams of Kief. A lb of mid grade suger leaf/popcorn but around 30 grams and a lb of low grade Shake/Trim around 20 to 25 grams. Now those numbers are not set in stone but it seems to me the user who did this would have needed well over a lb of good flower left to get that Kief on top of the 3 oz of bud they say they got. Does not seem possible looking at that plant. This is not a critique of your light but rather me just questioning the validity of what your customer told you and judging it by the size of the plant.
That said it's a good looking light with good specs.