What could an increase in systolic blood pressure and decrease in diastolic mean?
First, a couple of considerations 


Heart rate (HR) is lower when seating, and even lower when lying. I assume that participants were seated when the first measure was taken.
Cardiac output is not constant during the day. Depending on the moment, some factors such as digestion have an impact in Cardiac output, so take that into account when carrying out the experiments.


Normal walking may cause that blood pressure pattern. I think that you should not consider the increase in systolic pressure if it is not significant, as something as simple as crossing your legs when seated can increase your systolic pressure and normally diastolic pressure provides more information for physicians. Relaxation techniques usually decrease heart rate, which can affect the blood pressure. However, the point in this case seems to be that HR remains constant. I suppose that Mean Arterial Pressure $(MAP)$ has decreased.

If we part from:

$\textit{MAP} = (CO \cdot SVR) + CVP$
where $CO$ is cardiac output, $SVR$  is systemic vascular resistance and $CVP$ central venous pressure.

$CVP$ is usually depreciable. $CO$ is defined by $SV \cdot HR$, where $SV$ is the stroke volume. Then, if the HR is constant, only $SV$ or $SVR$ could have changed. Maybe the heart is pulsating more vigorously, or a vasodilation is decreasing $SVR$. I find the latter more likely. However, I don´t know why the smooth muscle could be relaxing. Make sure that heart rate is not changing and consider your sample size. 
I hope it helps, at least to focus you search on cardiac regulation. It is difficult to conclude anything without seeing the data but I tried to answer from my limited knowledge since I am not specialized in cardiac physiology.