Although we me see some immediate results from reducing our caloric intake, the main reason for the weight reduction is our reduction or carbohydrates or sugars (since we reduce all forms of nutrition). Carbohydrate intake causes our body to release insulin, an anabolic hormone released from the pancreas, that tells our body to store the excess sugars in our cells. Unfortunately our body has a limited amount of storage for these sugars and once that target is reached we store the remaining energy (calories) as triglycerides or adipose tissue. Therefore the reason our body puts on excess body weight is not due directly to an increase in caloric intake, but rather an over consumption of sugar that causes our body to be in a chronic state of anabolism (storing fat).
With this in mind we must then look at how we can use this to lose weight. When reducing our caloric intake on a diet, we typically eat healthier begin removing excess junk food (i.e chips, pop, candy). Since these all contain excess sugar that boosts our insulin levels, when we remove them we see this immediate loss of weight. However, we now go into a chronic state of low nutrition, which causes our body to want to keep what energy is left. This results in low blood sugar, which in turn tells our body we need to eat. To loss weight we must lower our carbohydrate and use foods that allow our bodies to have access to our stored excess energy. When eating a low carbohydrate meal, our body is now in a state of catabaolism, which allows us to access our adipose tissue as useable energy, rather than allows having access to simple sugars (a steady high level of insulin).
Although your workout may have caused some of the weight loss it is mainly attributed to the lower carbohydrate in tack caused by the lower overall intake. Your diet should be the main focus when attempting to lose weight, with less emphasis on which muscles are being used. A healthy active lifestyle normally correlates with a positive figure, but our diet is most import.
That being said, you should look into a lower-carbohydrate lifestyle consisting of healthy animal products and vegetables, while limiting our grain consumption and excess sugar, as well as processed vegetable oils.