Mysticoud, I think it is just luck of the draw sometimes. Girth work is unlikely to add more than .5” to your length but you can never be sure that you will gain no length. The head’s increase in size may add to the length a touch. The penis might also be predisposed to gaining more length than others might be. I don’t think you have to worry about gaining more than .5” in length from extensive work exclusively on girth exercises. The chances of you gaining zero length are quite good but nothing is ever certain.
I’l let the guys with experience of months on end of exclusive girth work step in now.