First John looks at Gross Sales of Gasoline i.e. including exports (not covered by the carbon tax) instead of the far more relevant and inclusive numbers of Net Sales of Gasoline + Net Sales of Diesel also included in the data table. Result:

2012->2015 Change in Gross Gasoline Sales: BC = +17%, Canada = +4%  - John's 6% is wrong
2012->2015 Net Gasoline+Diesel Sales: BC = -1.6%, Canada = +2.1%

Next he picks 2012 vs. 2015 instead of 2011 vs. 2015 the full scope of the data set to analyze a policy that was initiated in 2008. Adjust Date Range Result: 

2011->2015 Net Gasoline+Diesel Sales: BC = -11%, Canada = +.1%

The other major problem is he compares BC to Canada. This is a problem BC is part of Canada you need to compare BC to the rest of Canada to do a cross region comparison to normalize things like say the great recession that occurred during this time period.

2011->2015 Net Gasoline+Diesel Sales: BC = -11%, Rest of Canada = +4.3%