I took their word as truth as my travels through Mexico also revealed many more Christmas trees in the north compared to areas such as Mexico City and southern Mexico. I even wrote the December 2012 monthly travel photo post about Mexican Christmas trees.
Much to my detriment, however, I did not consult geographer and Mexico expert Tony Burton, co-author of Geo-Mexico, about this. His research indicates one (possibly two) Christmas Tree introductions to Mexico.
According to Burton, it seems that Emperor Maximillian brought over the Christmas Tree in the 1860s which then caught on with upper class Mexicans (most of whom in one way or another backed his government against the Liberal government of Benito Juarez). Some other sources Burton describes claim that Mexican General Miguel Negrete, who fought against Maximillian and the French, got the idea for a Christmas Tree from the United States in the 1870s.
I told several friends about the above and encountered reactions which hint at nationalist and local myths at play concerning the Christmas Tree in Mexico. An American economist friend who lived in Mexico laughed and said "Well, looks like Max did something." Meanwhile, a Mexico City-based Mexican friend stated that there was no way "any Mexican would dare copy Maximillian." Finally, a geographer in Monterrey could only reply with "but Christmas Trees came from the Germans [who immigrated to Monterrey]."
The second reaction reminded me of my visit to Chapultepec Castle when I asked a tour guide about the Mexican Conservatives who supported Maximillian. Apparently, at least at the museum, there is a strong nationalist myth that no Mexicans supported Maximillian, only the French did. After getting a stern message from the tour guide several Mexican tourists lectured me about how all Mexicans know Maximillian was a foreign puppet who had no true local support. Later, a Mexican friend told me that I might of well asked a Mount Vernon tour guide about George Washington profiting off stolen Loyalist property.
So is there a tie between the current-day myth that no Mexicans supported Maximillian and possible Hapsburg Christmas tree-denialism? Are the reports of General Negrete or German immigrants in the north introducing Christmas trees merely nationalist and local cover for adopting something the now hated Maximillian brought over from Europe? I honestly cannot say. There could have been easily multiple introduction of the Christmas tree to Mexico. However, the mystery remains and it is even a little bit fun to imagine a conspiracy behind the beloved Christmas tree.