Why could some egyptians take jobs other than farming

Because they might of been more skilled on the other jobs than farming. or because of their class in the egyptian time.

If there were ever any food surpluses, that would allow people to perform work other than farming because producing food was no longer a main focus.

A food surplus can occur when an excess production or supply over demand situation occurs. In this case, a lot of food could be left over from production time, allowing people to focus on things that do not have to produce the food, since the is no longer such a high demand where the supply is more than the demand.