What is the difference between a pastor and an administrator?
The difference can be large or small depending on the directives of the local bishop. If you recall, when Fr. Moore was ill, this parish had one administrator while Fr. Moore remained the official pastor. Under most circumstances there is virtually no difference in terms of what he can or cannot do. According to Church law:
When a parish is vacant, or when the parish priest is prevented from exercising his pastoral office in the parish by reason of imprisonment, exile or banishment, or by reason of incapacity or ill health or some other cause, the diocesan Bishop is as soon as possible to appoint a parochial administrator, that is, a priest who will take the place of the parish priest.
The parochial administrator is bound by the same obligations and has the same rights as a parish priest, unless the diocesan Bishop prescribes otherwise. The parochial administrator may not do anything which could prejudice the rights of the parish priest or could do harm to parochial property. When he has discharged his office, the parochial administrator is to give an account to the parish priest.
Thus while in Church law there is a difference between a pastor and an administrator, as a parishioner there is essentially no difference that anyone would notice.