Due to the process hinted at above, your weight in the short term is not directly beholden to the 3500 calories = 1 lb rule.
To see this in a very simple example, consider water. If you drink 16oz of water, you will in the short term gain 1 lb. Water has no calories so how is this possible? Simply because the weight of the water is added to you (the same as holding the water in a bottle), but as soon as you eliminate this water, you will of course weigh less.
The 3500 calories comes into your how your body processes food intake. As mentioned in the first reply, it is if you consume 3500 calories more than you require to survive, you will gain a lb or if you use 3500 more than you take in you will lose a lb. That is just a general number to help you see how much you have to cut to lose 1 lb of weight.
In reality, depending on the diet plan used, you could lose a lot of excess water. Or you could lose muscle, or you could lose fat, or you will likely lose some of all of them.
In the longer term, it mostly balances out. But still your intake vs your output can vary greatly.
The aforementioned steak will likely take a while to digest and will be eliminated over a period of time accordingly.