Of course. That does seem very likely and is *possibly* true. The problem is with Sheelas is that they were so insular and that there is nothing to compare them to in prehistory.
As I said somewhere else on this thread, it needs someone to pull a definite wooden Sheela out of a bog and dendro date it to a much earlier date than the stone ones can offer.
For them to sprout into being from nowhere seems very unlikely, but so far nothing can provide the evidence for this.
Glad you enjoyed Anthony's site in general. There aren't many like that around!