I think it is probable that journalists saw him leaving his home, just prior to him driving past the search site. The journalists seem to have been at his home when Gary Jubelin arrived a few minutes after Spedding left.
Unless Spedding stopped and gave the van to someone else to drive right after leaving his home, I think it was him driving his van past the search site.
Caption right under the picture:
A few minutes after Mr Spedding left his home (pictured) the head of the investigation, homicide Detective Inspector Gary Jubelin, was seen arriving at his house
There is even a picture in the link showing him waving at the journos, at the same time as this picture above was taken.
Police visit home of Bill Spedding in William Tyrrell case | Daily Mail Online