Well, sorry to have to tell you that you would not seem to have any case to appeal on based on your description. Your activity to collect some food from a restaurant would not be considered 'loading' by an adjudicator. However, tell us more about this food purchase, and it might fit into 'loading'. Something like bulky, weighty, pre-ordered are the attributes that could get this PCN cancelled.
I looked at the sign for the bay, and it is not restricted to goods vehicles, so anybody can park there to load, (or unload), but, for instance, just parking to pick-up a takeaway, would not usually count.
However, I may be completely wrong on this, so wait and see what the others say, but don't miss the deadline on the PCN for paying or submitting reps. There is no legal definition of 'loading', it is up to the judges, and adjudicators to decide what it is, and what it isn't.
