That's B.S.
Excommunication ferendæ sententiæ can be public only, as it must be the object of a declaratory sentence pronounced by a judge; but excommunication latæ sententiæ may be either public or occult. It is public through the publicity of the law when it is imposed and published by ecclesiastical authority; it is public through notoriety of fact when the offence that has incurred it is known to the majority in the locality, as in the case of those who have publicly done violence to clerics, or of the purchasers of church property. Catholic Encyclopdedia
but excommunication latæ sententiæ may be either public or occult.