This is a safety issue for both,those in the air and those on the ground. Would any pilot having to do an emergency landing choose a busy motorway and risk more lives. If he did, is it likely to lead to a criminal prosecution.
In this instance it remains to be determined whether after the failed aerobatic manoeuvre the pilot knew or should have known that his course was taking him towards a busy public highway and had the means to avoid it. In the event that no technical fault or malfunction affected the aircraft, then the only outcome can be that the aerobatic manoeuvre was not carried out with all the adequate planning required and generous margins for all unforeseen events and circumstances involved.