Actually, I would mind it, if they ran the Spanish flag up the pole, if it were done at a governmental site, and it was being flown in a place where the Stars and Stripes generally flies.
Now, if the Spanish flag, or a Mexican flag, were being flown at a consulate, or at a private residence (of *legal* residents), that would be fine.
Since the demonstrations of last year, the Mexican flag has taken on a different meaning. It has become a partisan emblem, or like the Confederate battle flag, a provocation. Few people would even recognize the Spanish flag.