Here is the law: http://www.diputados.gob.mx/LeyesBiblio/pdf/LGCT.pdf
I've done a bit more research on this, and from what I can tell, they're using Article 16 Section VI as their reasoning:
"Se prohibe:
VI. Comerciar, vender, distribuir, exhibir, promocionar o producir cualquier objeto que no sea un
producto del tabaco, que contenga alguno de los elementos de la marca o cualquier tipo de diseño o
señal auditiva que lo identifique con productos del tabaco."
In other words, it's prohibited to market things that aren't tobacco products in ways that associate them with tobacco products?
Also, the law appears to say absolutely nothing about owning or using these products--only importing or selling them.