That the bluestones came from Preseli has been known for a long time - a century? That they were there set up as a circle with an opening to the midsummer solstice sunrise, and the same circumference as Stonehenge was not. I think it has also been known for a while that some of the burials at Stonehenge were of people who grew up in Pembrokeshire.
It seems to me that if the people who built the Preseli circle decided for some reason to trek over to Salisbury Plain, then coming across the chalk ridges now defining the Avenue must have seemed like a sign that here was the place to rebuild. Like those folk myths about white cows lying down at the site for the future city. Much more understandable that some random person just happeneing to come across those ridges at the right time to spot their significant alignment, and thinking it was significant.