According to the Bureau of Labor Statistics, in 2000 the United States had roughly 1,310,000 jobs in the auto industry. Currently employment in the sector is around 800,000, implying a drop of 38.9 percent.
If employment in Canada followed the same pattern, then Mexico's share of total industry employment in North America would have risen to more than 55 percent if it had stayed constant since 2000. Since Mexico's share of total employment is now just 40 percent, it implies that it has gained share by seeing a less rapid decline, not by adding jobs. This doesn't fit well with the main thesis of the article which is that a middle class is rising in Mexico.
Total auto jobs are down, period.
And China has also lost a lot of manufacturing jobs.