I disagree. They were operating an ambulance without showing due regard. That is negligent.
The question is whether the "reasonably prudent" ambulance driver would check the front of the rig before pulling out of the bay. Since the "reasonably prudent" ambulance driver is, by definition, perfect and far more prudent than anyone who actually drives an ambulance, he doubtless would check what was right in front of him before he pulled out.
So, yes, off the cuff, knowing only the facts in the news article, I'd say there's a good case that there was some negligence here. The ambulance had a duty not to run patients over, they violated it, their violation was the proximate cause of the damages, and obviously, the guy who got run over was damaged. That's not to say it's a sure winner, but there certainly seems to be a case.