I thought I read Latino students in that school (or district) are in the mid-teens percentage. High enough IMO that it's shameful that school teachers would dress up as a border wall.
Personally, I agree with this sentiment. I don't automatically find that dressing up as Mexicans should be a cultural faux pas. Although I agree with those who've posted that it's still a professional environment so teachers should err on the side of caution, it is Halloween and I wouldn't judge "casual racism" without knowing more. As a progressive who is absolutely disgusted by the modern Republican party, charges of cultural appropriation can and do run amok IMHO. I.e. dressing up as a ninja if you aren't Japanese has been criticized, or the high school girl who decided to wear a Chinese evening dress to prom. As an Asian American, am I really supposed to be offended by these last two examples?
If the two pictures are from entirely different schools, then I think the first one remains ambiguous. But the very fact that it looks really bad in conjunction with the second one (which is downright inappropriate and offensive, as well as being hilariously un-self-aware with that Statue of Liberty reference) is surely a good illustration of why dressing up like that is just not a good idea. Even if you do it for apolitical 'humor' rather than a deliberate disrespect, consider the company you now find yourself in.
Maybe, also, one should keep distinct arguments about "cultural appropriation" and _mockery_? Those are different things and parody national-costumes are more the latter, surely? And thus could be said to belong to the wider category of 'blackface'.
And also I think that is dependent on the relationship between those who could be seen as engaging in 'mockery' and those potentially being mocked. It's not the same if the former don't have any power over the latter or any real history of interaction with them. Same reason why I don't think it would become an issue if I did a comedy American accent but could find myself in difficulties if I did a comedy Indian or Irish one.