Objection 1. It would seem that the seal of confession extends to other matters besides those which have reference to confession. For sins alone have reference to confession. Now sometimes besides sins other matters are told which have no reference to confession. Therefore, since such things are told to the priest, as to God, it seems that the seal of confession extends to them also.
Objection 2. Further, sometimes one person tells another a secret, which the latter receives under the seal of confession. Therefore the seal of confession extends to matters having no relation to confession.
On the contrary, The seal of confession is connected with sacramental confession. But those things which are connected with a sacrament, do not extend outside the bounds of the sacrament. Therefore the seal of confession does not extend to matters other than those which have reference to sacramental confession.
I answer that, The seal of confession does not extend directly to other matters than those which have reference to sacramental confession, yet indirectly matters also which are not connected with sacramental confession are affected by the seal of confession, those, for instance, which might lead to the discovery of a sinner or of his sin. Nevertheless these matters also must be most carefully hidden, both on account of scandal, and to avoid leading others into sin through their becoming familiar with it.
This suffices for the Reply to the First Objection.
Reply to Objection 2. A confidence ought not easily to be accepted in this way: but if it be done the secret must be kept in the way promised, as though one had the secret through confession, though not through the seal of confession.
Source: Summa Theologica (New Advent)