I'm guessing it's the amount of carbs you consumed and the insulin you injected was not enough or not getting through. If I was to eat porridge, followed by toast followed by more bread then I would need a lot of insulin for it as a type 1 regardless of how far I ran (and I run every day). I know you have insulin to hand and forgive me for stereotyping here, but if you are a type 2 it may be that you are also insulin resistant meaning your 5 units is doing very little. As for the walk, well generally speaking it does help to lower levels but only up to a certain point. Also, sometimes levels go up after exercise but usually when it's vigorous or for a prolonged period of time. I am having to guess in your circumstances but that would be my theory. How are your levels ordinarily after your meals?