OP, we can dispense with your concerns regarding 'footpath', because it isn't, instead your contravention was the second limb of the grounds 'or part of a road other than a carriageway' AKA footway.
You waited on the footway for approx. 20 minutes in total although the PCN refers to a specific moment in time.
And your reason for being there was?
Do you remember when you left?
Pl post the back of the PCN.