I think it is reasonably clear that the preschool is in a separate building.
The picture on their website locates the space that they use in a separate building to the church building. I don’t think they would have a directions type photo with the wrong location.
They also describe the location as:
Getting to Explorer
Explorer Preschool is located at 2700 Booksin Avenue, San Jose. We lease our space from Lincoln Glen Church and are located directly behind West Hills Church.
I,ve marked in green the Lincoln Glen Church, in yellow West Hills Church and in red a separate building which is where the school is based on their pin and description.
There is clear separation between the 2 buildings.
I do think we need to be clear with the language we use. This is a church with a large property all at the one address with 3 separate uses one of which has a pre-school in one of its buildings,