In Walmart your effective pressure ("mean") was nearly 110.
At home, it was nearly 93. Those are the figures you need to look at. Although you don't say what your pulse rate was (and for accuracy you really do need those) they tell you how much work your heart was doing at the two times, and clearly, you were doing much more at Walmart, and your B/P readings reflect that very well. - It wasn't "white coat" effect. It was true physical stress
The machines are in fact very accurate, IF YOU USE THE SAME ONES all the time, and provided you measure at the same spot every time.
But remember, the actual numbers you read don't signify a plug nickel. They are neither real, nor true, nor comparable with anybody else's.
But CHANGES are real, true and accurate. That is, -if, ON YOU OWN MACHINE, you get a change, then that INDICATES a real, true, actual change in the pressure generated within the left ventricle of our heart.
EDIT: thank you. Your pulse rate figures show that you were doing 1.63 times the work in your Walmart travels than you were doing at home, so the numbers you quote fit in perfectly with this.
There's nothing abnormal nor unusual now. -Ignore the numpties who say there is. You're fine.