AI would guess dowels to support the layer on top were inserted through each apple and the cake underneath.
I would agree that the dowelling runs through the apples and the cake beneath.
I also think that you would have to put some sort of a barrier between the apple and the fondant or else the juice from the apples would I imagine not only melt away the fondant in patches but also discolour it when the juice oxidises with the air.
Maybe the apple is pierced well before it goes on the cake so that it has a chance to dry out a bit and then a little white chocolate?? is placed on the cake or something.
Another possibility are that they are really good quality fake fruit that has had a hole drilled in them for the dowel to run through.
If the dowels are in well and the apples are really inly there to ensure that the cake doesn't tip and not to take the weight of the cake then although I wouldn't move the cake like that I don't think it would be likely to come crashing down.
Very interesting, let us know how you go.
The decorator who made my wedding cake has done this one. Luckily he is also my sisters father in law and I emailed him to ask, he said pretty much the same as others, doweling through the apples and the next cake balanced on top. He also said he went through ALOT of apples finding ones with the flattest bottoms.