This is ridiculous, why would the law allow ignorance to be an excuse? It's the responsibility of a driver to make sure what they're doing is safe. By this logic I could just drive around not checking my mirrors anywhere and be able to get off scot free for any accidents I cause.
Many HTA offences are absolute liability offences. To be convicted, there is no need to prove the you willfully intended to do it. The Crown just needs prove that you did it, and no excuses for why you did it would matter.
Other offences require the Crown to prove that you actively intended to commit the act, in other words, that you had mens rea or guilty mind. Failure to remain and failure to render aid fall into this category. If you know you are in a crash, you have a duty to stop and if necessary render aid. However, if you were not even aware that a crash had occurred, then how could you be guilty of deliberately
choosing to leave the crash scene or not render aid? The Crown will have to somehow prove that he was aware a crash had happened.
This is different from you driving around and not checking your mirrors. You have a duty to be aware of traffic around you. Being ignorant of the presence of other traffic is not a defence if you hit them because you failed to take reasonable care, such as checking mirrors and blind spots. This is where a careless driving charge can come in.
However, there is a potential out even on this charge if you can manage to show to the court that you DID take reasonable care to look for traffic around you, but the person you hit was driving/riding well outside the realm of what you would reasonably be expected to look out for. Probably the most common example of this is a left-turner making a turn in what he thought was enough room, only to run into oncoming warp-boy travelling at speeds high above the speed limit and above what would be reasonably expected at that location.
With respect to this particular crash and the careless driving charge, it's even possible that a JP might side with the driver if the driver's lawyer is able to successful argue that there was no reasonable expectation for a moving vehicle to be at the driver's right rear in a lane occupied with parked cars. As far as charges and prospect of conviction go, this one is not as cut and dry as some might think.