"Oops". That's what the driver of the silver car said - or something like that I imagine. When reversing, or doing any manoeuvre where your view is less than ideal, think where your biggest danger might be coming from. Lots of drivers reverse out of spaces using just their mirrors which would be great if the dangers were immediately behind you!
It's important to look mainly in the direction you're going (actually turn and look with your eyes!) ; you wouldn't look out of the back window when you're driving forward - would you? Twisting around in your seat is awkward and uncomfortable, but it's the only way you can get a really good view out of the back window and, crucially, your blind spots to the left and right.
There's another important point here too. We owe it to ourselves and others to pay attention - because people make mistakes. Car parks are not the open road; you need to be super-cautious. Here it's a typical car park prang. Think though, what if a toddler ran out? Could you stop in time? As my mum used to say when I was a naughty boy 'think on lad...think on'.