A change in your lifestyle can definitely affect your blood pressure. This degree of change in blood pressure is quite unexpected. In my experience, lifestyle modification changes blood pressure only by about 10-15%. However, there are unusual cases. (I know someone who had a cholesterol
way over 300, who got it down below 200 just by changing his diet. But before he changed his diet, he was eating two dozen eggs per day.)
I guess my question to you would be how much coffee were you drinking? If it was just one cup, then that would not explain this degree of change. If it was a pot of coffee or two, then this is probably the most significant change you have made. Or perhaps you have significantly reduced your stress
level recently? Perhaps that is the key. If so, the change may be dependant on whether that stress tends to be recurrent in your life.
But how are you getting your blood pressure readings if you are not seeing a doctor? Perhaps the first readings were not accurate? Blood pressure readings are affected by how and when you take them. Sitting with your legs crossed increases the reading. Sitting in a chair with no back increases the reading. Not having your arm resting on a table or arm of a chair can increase the reading. Taking your blood pressure when you need to pee can increase the reading. As you can see, many things can increase your readings artificially.
If you are using a home blood pressure monitoring device, it might be worth getting the pressure double checked at least once by taking it at one of those blood pressure machines they have at many pharmacies. If it registers the same, I would say the change is probably real. I do think that it would still be advisable to continue to exercise regularly and eat right regardless. This is a heart healthy lifestyle that will definitely pay off in the end.