Demonic deception, since heresy is being promoted.
Strong opinion... Be careful of what you say though
If you're asking an Orthodox about Lourdes, and the Immaculate Conception is part and parcel of this apparition, why should he be careful of judging it to be demonic deception? After all, it is not an Orthodox teaching, so obviously it's not coming from God.
According to my understanding of the Roman Catholic Church's position on these matters, no one need believe in any "private revelations", even if they have some level of ecclesiastical approval (and it is a rather apophatic approval at that). You can disregard them all, even if the messages are not contrary to the faith. If they are contrary to the faith, all the more reason to dismiss them.
The strong, devoted faith that certain types of RC's put in such experiences and the people who claim to have them, as if they were a parallel source of revelation and magisterial authority, troubles me more than even some of the visions themselves. And the "official" Church bears part of the blame for that. On the one hand, they don't require the acceptance of private revelations, but on the other hand feasts commemorating some of these visions or the devotions they promote are placed on the universal liturgical calendar, requiring that they are accepted in some way by the Church.