HBStowe
The mental lapse required is really not that bizarre. He knows of that trope, it's just not right at the front of his mind permeating every thought.
If you have suffered from racism, it probably is right at the front of your mind permeating many thoughts.
Or if someone is a massive racist, it probably is right at the front of their mind permeating everything.
For a lot of people, that information is buried a few layers deeper, and unless something triggers it, it just stays there undisturbed.
I still think most people will see it after a second or two, but it's not that crazy that some people will miss it completely, especially when you consider that it's a chimp in the picture (not a monkey) so it's a little further removed from the common tropes, and also when you consider that a lot of people won't have in the front of their mind that MM is mixed race. Clearly she is, and mixed race people may well be proud of that and carry thought with them often when they see her. But I think a lot of people will, mots of the time, just see a person, and her race doesn't even occur to them. Again, of course they probably know her heritage, but there is a difference between having the information in their brain, and that information actually being in someone's thoughts.