I eat a vegan diet, as WFPB as I can, and in my experience--I am a cardiac patient with a history of a heart attack and triple bypass, what you're doing is one of the best, most pro-active things you can do. i've been eating this way a little over 3 years now and I'm not taking any medications for related to any of my coronary issues.
You didn't state how often you take your BP, or what you BP was at the starting point of your new diet was. Keeping a record of your BP, especially if you take it a few times daily will give you a much better idea of what is going on than just a single data point. Your diastolic was the same for both readings you gave and the 20 point difference in the systolic certainly could be a daily variation. I also take my records with me to my annual cardio check up . I've kept track of my daily BP in a log that also includes my physical activity, and sleep. I got in the habit 3 1/2 years ago from cardiac rehab.
One thing you can do is after you take your BP readings is then sit there and breath in and out slowly and deeply and then retake it. In rehab taking a BP immediately after exercise then doing this I was, on average able to reduce my systolic 8-10 points. Keep in mind though, this would also be a side effect of regular exercise, your recovery time is much quicker.
One other thing I wanted to ask you is if you're following any particular WFPB diet, such as the Esselstyn protocol, no oil, no salt, etc? Not all WFPB diets are the same depending on one's issues. Keeping track of one's sodium intake can be interesting. I don't notice much difference at all, while I know other cardiac patients that do. I don't however keep track of mg of sodium, so my definition of a high salt meal is subjective.
Losing the extra weight is good. If you are increasing your physical activity, that is also good. If you care to share a little more detailed information, I may be able to be more helpful.
Best to you,