I thought all the upper echelons in Mexico, including the president, were traditionally involved in the drug trade. I suspect this fellow must have been disagreeable and made himself unpopular with his fellows, like Shelley in California.
I have no doubt that you're right on target, although I wonder why they didn't just 'disappear him'....less negative international press. Perhaps it was going to blow up in their faces anyway and this is some sort of damage control? We'll never know the truth, of course, and the Mexican people will continue to starve and live lives full of misery and pain.