At the present time a lot of remarks about Mexicans are made that are not based on facts but rather for the sake of hate, so moderators can require utmost care when it comes to posts about Mexicans in a negative daylight.
Now when it comes to the statement itself, I cannot verify your statement so I can't tell if it's fact for fiction, but that doesn't really matter to me. I place really little value in numbers, since numbers only tell a part of the story, and only when I know why the numbers are the way they are I can start drawing conclusions, without the story behind the numbers, numbers only form a half-truth, and half-truths, although not lies by themselves easily lead to people drawing wrong conclusions, and I guess the responsible moderator (whoever it was), was not really willing to risk that, this due to the sensitivity on the subject of Mexico and Mexicans... well, at least within the United States. The meme does not directly state it, but to the moderator it may easily imply Mexicans, as a group of people (and thus not judging per individual), are murderous maniacs, and I think that implication was what caused the moderator to act. Question is of course also in which stream you tried to post this meme, since some streams may be stricter than others.
Please note, I am not expressing my personal opinion about the meme itself, neither will I express werther or not this moderator is in error. Since I've moderated many communities myself and may even moderate communities in the future, I prefer to take a neutral position when it comes to what a moderator does and does not. I am merely trying to give an interpretation to what may have moved this moderator to do what they did, and why they may have deemed that particular meme "racist".
Also note that when it comes to racism on the internet, more and more countries require communities to moderate on this in a stricter manner, and particularly when it comes to sites serving as social media. IMGFLIP cannot risk getting banned in several countries due to "poor moderation" on this department, so they'd rather be too careful than too lenient.
I hope this may clarify things a bit....