That is not surprising. I also doubt you would get the same benefit by just taking a capsule or juicing. Because you will likely undo that benefit by eating more unhealthy animal based foods again that will increase cholesterol and blood pressure. Eating that much celery meant you had to cut down on milk derivatives and meat by the 1/4 lb. of celery you ate.
I would instead recommend sticking to the advice of some of the following experts:
Dr. Caldwell Esselstyn, Dr. Neil Bernard, Dr. John McDougall, Dr. Joel Fuhrman who all advocate whole foods plant based diets to reverse such conditions as high blood pressure. If you do that you will get even better results.