This depends on a number of things like what you ate, what you were doing before you ate, how you treat your diabetes, what drugs you take, whether you had any carb residue on your fingers when you took your readings and and how fast you walked.
Given there are so many things which can affect a BG reading, I don't spend too much time worrying about a single oddity: like all good experiments, I check it is repeatable over similar circumstances.
But to answer your question, for me, as type 1 treated by insulin, I have often see my BG fall much faster than this.