Interesting case. I would agree that if someone started a fire out of negligence (ie unattended fire), then they should be held liable in some way for the damage done, especially given the significant problems we've had in Canada the last few years with wildfires, and the likelihood that we will continue to experience these problems.
I guess it really boils down to where the line is for negligence, and it seems like the courts have ruled he should have done more to ensure it was under control and fully extinguished before leaving and not returning to site. To be honest, him not realizing that fires can go underground seems kinda dumb to me, considering he was burning brush from his land. Fire is an enormous danger -if you don't know how to do large, controlled burns over extended periods of time, consult firefighters first and/or the local government so at least your ass is covered and you can say "I did what the experts told me to do."